Make headline images explicit, add asset credits

- related_assets gains a `headline` boolean (DB-enforced: at most one
  per page), replacing "first image by position" as the headline
  rule. A rake task backfills the current first image on every live
  head/draft, so nothing changes visually until an editor changes it.
- The image picker sidebar gets a star toggle reflecting the flag;
  the TinyMCE inline-image picker's badge now reads it too, instead
  of assuming position 0.
- No headline chosen (or none attached) now falls back to the
  gallery-count caption itself becoming the lightbox trigger, instead
  of the gallery being unreachable.
- Assets gain creator, source_url, and license_key (against a new
  config/asset_licenses.yml dictionary). asset_credit renders a
  degrading attribution line, reused as a hidden per-image glightbox
  caption so credit is one click away for every image, not only the
  headline's always-visible one.
- Fixed: asset thumbnails rendered unconditionally regardless of
  whether a real variant exists on disk. Asset#has_variant? checks
  file existence, not content type -- some legacy PDFs have real
  pre-rewrite thumbnails a content-type check would have hidden.
- assets#new/edit rebuilt onto the same node_description/node_content
  layout as assets#show, picking up the three new fields in the
  process.

35 files changed, 592 insertions, 91 deletions

diff --git a/app/controllers/assets_controller.rb b/app/controllers/assets_controller.rb
index d150e06..becfe13 100644
--- a/app/controllers/assets_controller.rb
+++ b/app/controllers/assets_controller.rb
@@ -89,6 +89,6 @@ class AssetsController < ApplicationController
   private
 
     def asset_params
-      params.require(:asset).permit(:name, :upload)
+      params.require(:asset).permit(:name, :upload, :creator, :source_url, :license_key)
     end
 end
diff --git a/app/controllers/related_assets_controller.rb b/app/controllers/related_assets_controller.rb
index 5af73fc..da82cde 100644
--- a/app/controllers/related_assets_controller.rb
+++ b/app/controllers/related_assets_controller.rb
@@ -39,7 +39,17 @@ class RelatedAssetsController < ApplicationController
   end
 
   def update
-    @node.editable_page.related_assets.find(params[:id]).insert_at(params[:position].to_i)
+    related = @node.editable_page.related_assets.find(params[:id])
+
+    if params.key?(:headline)
+      RelatedAsset.transaction do
+        @node.editable_page.related_assets.update_all(headline: false)
+        related.update!(headline: true) if params[:headline] == "true"
+      end
+    else
+      related.insert_at(params[:position].to_i)
+    end
+
     head :ok
   end
 
diff --git a/app/helpers/content_helper.rb b/app/helpers/content_helper.rb
index 5810966..5b67259 100644
--- a/app/helpers/content_helper.rb
+++ b/app/helpers/content_helper.rb
@@ -53,11 +53,8 @@ module ContentHelper
   end
 
   def headline_image
-    @images = @page.assets.images
-
-    unless @images.empty?
-      render :partial => 'content/headline_image'
-    end
+    @headline_asset = @page.related_assets.find_by(headline: true)&.asset
+    render :partial => 'content/headline_image' if @headline_asset || @page.assets.images.any?
   end
 
   # Returns the published_at attribute of a page if it is not nil, otherwise
@@ -154,4 +151,26 @@ module ContentHelper
     )
   end
 
+  def asset_credit(asset)
+    return nil unless asset
+    return nil if asset.creator.blank? && asset.source_url.blank? && asset.license_key.blank?
+
+    license = AssetLicense.find(asset.license_key)
+
+    photo_label = t("asset_credits.photo", name: asset.name)
+    photo = asset.source_url.present? ? link_to(photo_label, asset.source_url) : photo_label
+
+    attribution_parts = [photo]
+    attribution_parts << t("asset_credits.by", creator: asset.creator) if asset.creator.present?
+    attribution = safe_join(attribution_parts, " ")
+
+    license_text = if license
+      name = t("asset_licenses.#{license.key}", default: license.key)
+      phrase = license.style == "license" ? t("asset_credits.licensed_under", license: name) : name
+      license.url.present? ? link_to(phrase, license.url) : phrase
+    end
+
+    full = license_text ? safe_join([attribution, license_text], ", ") : attribution
+    safe_join([full, "."])
+  end
 end
diff --git a/app/models/asset.rb b/app/models/asset.rb
index aca0ee8..8bea1b3 100644
--- a/app/models/asset.rb
+++ b/app/models/asset.rb
@@ -1,12 +1,18 @@
 class Asset < ApplicationRecord
+  IMAGE_CONTENT_TYPES = ["image/gif", "image/jpeg", "image/png", "image/webp"]
 
   include FileAttachment
   
   has_many :related_assets, :dependent => :destroy
   has_many :pages, :through => :related_assets
 
-  scope :images,    -> { where(:upload_content_type => ["image/gif", "image/jpeg", "image/png", "image/webp"]) }
+  scope :images,    -> { where(:upload_content_type => IMAGE_CONTENT_TYPES) }
   scope :documents, -> { where(:upload_content_type => ["application/pdf", "text/plain", "text/rtf"]) }
   scope :audio,     -> { where(:upload_content_type => ["audio/mpeg", "audio/x-m4a", "audio/wav", "audio/x-wav"]) }
 
+  validates :license_key, inclusion: { in: -> { AssetLicense.keys } }, allow_blank: true
+
+  def image?
+    IMAGE_CONTENT_TYPES.include?(upload_content_type)
+  end
 end
diff --git a/app/models/asset_license.rb b/app/models/asset_license.rb
new file mode 100644
index 0000000..ca66d40
--- /dev/null
+++ b/app/models/asset_license.rb
@@ -0,0 +1,15 @@
+class AssetLicense
+  Entry = Struct.new(:key, :url, :requires_attribution, :style, keyword_init: true)
+
+  DICTIONARY = YAML.load_file(Rails.root.join("config", "asset_licenses.yml")).freeze
+
+  def self.keys
+    DICTIONARY.keys
+  end
+
+  def self.find(key)
+    entry = DICTIONARY[key.to_s] if key.present?
+    return nil unless entry
+    Entry.new(key: key.to_s, url: entry["url"], requires_attribution: entry["requires_attribution"], style: entry["style"])
+  end
+end
diff --git a/app/models/concerns/file_attachment.rb b/app/models/concerns/file_attachment.rb
index 3c09456..e7a33c5 100644
--- a/app/models/concerns/file_attachment.rb
+++ b/app/models/concerns/file_attachment.rb
@@ -52,6 +52,14 @@ module FileAttachment
     build_upload_proxy
   end
 
+  def has_variant?(style)
+    upload_file_name.present? && File.exist?(file_path(style))
+  end
+
+  def previewable?
+    has_variant?(:medium)
+  end
+
   private
 
   def build_upload_proxy
diff --git a/app/models/related_asset.rb b/app/models/related_asset.rb
index 8f16460..62000cc 100644
--- a/app/models/related_asset.rb
+++ b/app/models/related_asset.rb
@@ -5,4 +5,13 @@ class RelatedAsset < ApplicationRecord
   acts_as_list :scope => :page_id
 
   default_scope -> { order("position ASC") }
+
+  validate :headline_only_for_images
+
+  private
+
+    def headline_only_for_images
+      return unless asset
+      errors.add(:headline, "can only be set on image assets") if headline? && !asset.image?
+    end
 end
diff --git a/app/views/assets/edit.html.erb b/app/views/assets/edit.html.erb
index f198600..3ef8fea 100644
--- a/app/views/assets/edit.html.erb
+++ b/app/views/assets/edit.html.erb
@@ -1,24 +1,44 @@
-<h1>Editing asset</h1>
+<div id="page_editor">
+  <h1>Editing asset</h1>
 
-<%= form_for(@asset, html: { multipart: true }) do |f| %>
-  <%= form_error_messages(f) %>
+  <%= form_for(@asset, html: { multipart: true }) do |f| %>
+    <%= form_error_messages(f) %>
 
-  <% if @asset.upload.present? %>
-    <p>
-      <strong>Current file:</strong>
-      <%= @asset.upload.url %>
-      (<%= number_to_human_size(@asset.upload.size) %>)
-    </p>
-  <% end %>
+    <div id="content">
+      <div class="node_description"><%= f.label :name %></div>
+      <div class="node_content"><%= f.text_field :name %></div>
+
+      <% if @asset.upload.present? %>
+        <div class="node_description">Current File</div>
+        <div class="node_content"><%= @asset.upload.url %> (<%= number_to_human_size(@asset.upload.size) %>)</div>
+      <% end %>
+
+      <div class="node_description"><%= f.label :upload, "Replace file" %></div>
+      <div class="node_content"><%= f.file_field :upload %></div>
 
-  <p>
-    <label>Replace file:</label><br>
-    <%= f.file_field :upload %>
-  </p>
+      <div class="node_description"><%= f.label :creator %></div>
+      <div class="node_content"><%= f.text_field :creator %></div>
 
-  <p>
-    <%= f.submit 'Update' %>
-  </p>
-<% end %>
+      <div class="node_description"><%= f.label :source_url, "Source URL" %></div>
+      <div class="node_content"><%= f.text_field :source_url %></div>
 
-<%= link_to 'Show', @asset %> | <%= link_to 'Back', assets_path %>
+      <div class="node_description"><%= f.label :license_key, "License" %></div>
+      <div class="node_content">
+        <%= f.select :license_key,
+              options_for_select(
+                [["— none —", ""]] + AssetLicense.keys.map { |key| [t("asset_licenses.#{key}"), key] },
+                @asset.license_key
+              ) %>
+      </div>
+
+      <div class="node_description">Actions</div>
+      <div class="node_content node_info_group">
+        <div class="node_info_group_items">
+          <div class="node_info_item"><%= f.submit 'Update' %></div>
+          <div class="node_info_item"><%= link_to 'Show', @asset %></div>
+          <div class="node_info_item"><%= link_to 'Back', assets_path %></div>
+        </div>
+      </div>
+    </div>
+  <% end %>
+</div>
diff --git a/app/views/assets/index.html.erb b/app/views/assets/index.html.erb
index 8c35561..ff1300a 100644
--- a/app/views/assets/index.html.erb
+++ b/app/views/assets/index.html.erb
@@ -17,7 +17,7 @@
   </tr>
 <% @assets.each do |asset| %>
   <tr>
-    <td><%= image_tag asset.upload.url(:thumb), style: "max-width: 100px; max-height: 100px;" %></td>
+    <td><% if asset.has_variant?(:thumb) %><%= image_tag asset.upload.url(:thumb), style: "max-width: 100px; max-height: 100px;" %><% end %></td>
     <td><%= link_to asset.name, asset.upload.url %></td>
     <td><%= asset.upload.content_type %></td>
     <td><%= link_to 'Show', asset %></td>
diff --git a/app/views/assets/new.html.erb b/app/views/assets/new.html.erb
index 6c1310a..2cf8865 100644
--- a/app/views/assets/new.html.erb
+++ b/app/views/assets/new.html.erb
@@ -1,17 +1,38 @@
-<h1>New asset</h1>
+<div id="page_editor">
+  <h1>New asset</h1>
 
-<%= form_for(@asset, :html => { :multipart => true }) do |f| %>
-  <%= form_error_messages(f) %>
-  
-  <p>
-    <%= f.label :name %><br />
-    <%= f.text_field :name %>
-  </p>
+  <%= form_for(@asset, :html => { :multipart => true }) do |f| %>
+    <%= form_error_messages(f) %>
 
-  <p>
-    <%= f.file_field :upload %>
-    <%= f.submit 'Create' %>
-  </p>
-<% end %>
+    <div id="content">
+      <div class="node_description"><%= f.label :name %></div>
+      <div class="node_content"><%= f.text_field :name %></div>
 
-<%= link_to 'Back', assets_path %>
+      <div class="node_description"><%= f.label :upload, "File" %></div>
+      <div class="node_content"><%= f.file_field :upload %></div>
+
+      <div class="node_description"><%= f.label :creator %></div>
+      <div class="node_content"><%= f.text_field :creator %></div>
+
+      <div class="node_description"><%= f.label :source_url, "Source URL" %></div>
+      <div class="node_content"><%= f.text_field :source_url %></div>
+
+      <div class="node_description"><%= f.label :license_key, "License" %></div>
+      <div class="node_content">
+        <%= f.select :license_key,
+              options_for_select(
+                [["— none —", ""]] + AssetLicense.keys.map { |key| [t("asset_licenses.#{key}"), key] },
+                @asset.license_key
+              ) %>
+      </div>
+
+      <div class="node_description">Actions</div>
+      <div class="node_content node_info_group">
+        <div class="node_info_group_items">
+          <div class="node_info_item"><%= f.submit 'Create' %></div>
+          <div class="node_info_item"><%= link_to 'Back', assets_path %></div>
+        </div>
+      </div>
+    </div>
+  <% end %>
+</div>
diff --git a/app/views/assets/show.html.erb b/app/views/assets/show.html.erb
index ff00883..a0e4e46 100644
--- a/app/views/assets/show.html.erb
+++ b/app/views/assets/show.html.erb
@@ -17,7 +17,10 @@
     </div>
 
     <div class="node_description">Thumbnail</div>
-    <div class="node_content"><%= image_tag @asset.upload.url(:medium), style: "max-width: 300px; max-height: 300px;" %></div>
+    <% if @asset.has_variant?(:medium) %>
+      <div class="node_description">Thumbnail</div>
+      <div class="node_content"><%= image_tag @asset.upload.url(:medium), style: "max-width: 300px; max-height: 300px;" %></div>
+    <% end %>
 
     <div class="node_description">Public Path</div>
     <div class="node_content">
@@ -30,6 +33,27 @@
       </button>
     </div>
 
+    <div class="node_description">Creator</div>
+    <div class="node_content"><%= @asset.creator.presence || "—" %></div>
+
+    <div class="node_description">Source</div>
+    <div class="node_content">
+      <% if @asset.source_url.present? %>
+        <%= link_to @asset.source_url, @asset.source_url %>
+      <% else %>
+        —
+      <% end %>
+    </div>
+
+    <div class="node_description">License</div>
+    <div class="node_content">
+      <% if (license = AssetLicense.find(@asset.license_key)) %>
+        <%= t("asset_licenses.#{license.key}") %>
+      <% else %>
+        —
+      <% end %>
+    </div>
+
     <div class="node_description">Content Type</div>
     <div class="node_content"><%= @asset.upload.content_type %></div>
 
diff --git a/app/views/content/_asset_credits.html.erb b/app/views/content/_asset_credits.html.erb
new file mode 100644
index 0000000..85739d0
--- /dev/null
+++ b/app/views/content/_asset_credits.html.erb
@@ -0,0 +1,12 @@
+<% if @page.assets.images.any? %>
+  <div id="asset_credits">
+    <% @page.assets.images.each do |image| %>
+      <% credit = asset_credit(image) %>
+      <% next unless credit %>
+      <div id="credit_for_asset_<%= image.id %>"
+           class="glightbox-desc<%= " headline_credit" if image == @headline_asset %>">
+        <%= credit %>
+      </div>
+    <% end %>
+  </div>
+<% end %>
diff --git a/app/views/content/_headline_image.html.erb b/app/views/content/_headline_image.html.erb
index 243be40..c764d22 100644
--- a/app/views/content/_headline_image.html.erb
+++ b/app/views/content/_headline_image.html.erb
@@ -1,16 +1,28 @@
-<%= link_to(
-  image_tag(@images[0].upload.url(:headline)),
-  @images[0].upload.url,
-  :class => "glightbox",
-  :data  => { :gallery => "page-#{@page.node.id}" }
-) %>
+<% gallery_images = @page.assets.images %>
 
-<% if 1 < @images.length %>
-  <div class="right">
-    <%= "#{@images.length} #{t(:images)}" %>
-  </div>
+<% if @headline_asset %>
+  <%= link_to(
+    image_tag(@headline_asset.upload.url(:headline)),
+    @headline_asset.upload.url,
+    :class => "glightbox",
+    :data  => { :gallery => "page-#{@page.node.id}", :title => @headline_asset.name,
+                :description => "#credit_for_asset_#{@headline_asset.id}" }
+  ) %>
+  <% if gallery_images.size > 1 %>
+    <div class="right"><%= "#{gallery_images.size} #{t(:images)}" %></div>
+  <% end %>
+<% elsif gallery_images.any? %>
+  <%= link_to "#{gallery_images.size} #{t(:images)}, #{t(:open_gallery)}",
+        gallery_images.first.upload.url,
+        :class => "glightbox right",
+        :data  => { :gallery => "page-#{@page.node.id}", :title => gallery_images.first.name,
+                    :description => "#credit_for_asset_#{gallery_images.first.id}" } %>
 <% end %>
 
-<% @images[1..-1].each do |image| %>
-  <%= link_to "", image.upload.url, :class => "glightbox", :style => "display: none", :data => { :gallery => "page-#{@page.node.id}" } %>
+<% gallery_images.each do |image| %>
+  <% next if image == @headline_asset %>
+  <% next if !@headline_asset && image == gallery_images.first %>
+  <%= link_to "", image.upload.url, :class => "glightbox", :style => "display: none",
+        :data => { :gallery => "page-#{@page.node.id}", :title => image.name,
+                   :description => "#credit_for_asset_#{image.id}" } %>
 <% end %>
diff --git a/app/views/custom/page_templates/public/chapter_detail.html.erb b/app/views/custom/page_templates/public/chapter_detail.html.erb
index c4c2598..18449b8 100644
--- a/app/views/custom/page_templates/public/chapter_detail.html.erb
+++ b/app/views/custom/page_templates/public/chapter_detail.html.erb
@@ -31,4 +31,5 @@
       </ul>
     </div>
   <% end %>
+  <%= render partial: 'content/asset_credits' %>
 </div>
diff --git a/app/views/custom/page_templates/public/no_date_and_author.html.erb b/app/views/custom/page_templates/public/no_date_and_author.html.erb
index fa39e54..ec7e850 100644
--- a/app/views/custom/page_templates/public/no_date_and_author.html.erb
+++ b/app/views/custom/page_templates/public/no_date_and_author.html.erb
@@ -3,6 +3,7 @@
   <p><%= sanitize( @page.abstract ) %></p>
   <div id="headline_image"><%= headline_image %></div>
   <%= aggregate?(@page.body) %>
+  <%= render partial: 'content/asset_credits' %>
 </div>
 
 <%= will_paginate(@content_collection) if @content_collection %>
diff --git a/app/views/custom/page_templates/public/no_title_abstract_date_and_author.html.erb b/app/views/custom/page_templates/public/no_title_abstract_date_and_author.html.erb
index 64e2a7c..c486684 100644
--- a/app/views/custom/page_templates/public/no_title_abstract_date_and_author.html.erb
+++ b/app/views/custom/page_templates/public/no_title_abstract_date_and_author.html.erb
@@ -1,6 +1,7 @@
 <div class="article" lang="<%= @page.effective_lang %>">
   <div id="headline_image"><%= headline_image %></div>
   <%= aggregate?(@page.body) %>
+  <%= render partial: 'content/asset_credits' %>
 </div>
 
 <%= will_paginate(@content_collection) if @content_collection %>
diff --git a/app/views/custom/page_templates/public/standard_template.html.erb b/app/views/custom/page_templates/public/standard_template.html.erb
index bbc8cd0..e1e2eb0 100644
--- a/app/views/custom/page_templates/public/standard_template.html.erb
+++ b/app/views/custom/page_templates/public/standard_template.html.erb
@@ -3,6 +3,7 @@
   <div class="abstract"><p><%= sanitize( @page.abstract )%></p></div>
   <div id="headline_image"><%= headline_image %></div>
   <div class="body"><%= aggregate?(@page.body) %></div>
+  <%= render partial: 'content/asset_credits' %>
 </div>
 
 <%= will_paginate(@content_collection) if @content_collection %>
diff --git a/app/views/custom/page_templates/public/title_only.html.erb b/app/views/custom/page_templates/public/title_only.html.erb
index 42fe9a6..d706e9d 100644
--- a/app/views/custom/page_templates/public/title_only.html.erb
+++ b/app/views/custom/page_templates/public/title_only.html.erb
@@ -2,6 +2,7 @@
   <h2 class="headline"><%= @page.title %></h2>
   <div id="headline_image"><%= headline_image %></div>
   <%= aggregate?(@page.body) %>
+  <%= render partial: 'content/asset_credits' %>
 </div>
 
 <%= will_paginate(@content_collection) if @content_collection %>
diff --git a/app/views/custom/page_templates/public/update.html.erb b/app/views/custom/page_templates/public/update.html.erb
index d5995ac..0ff1bb2 100644
--- a/app/views/custom/page_templates/public/update.html.erb
+++ b/app/views/custom/page_templates/public/update.html.erb
@@ -4,6 +4,7 @@
   <div class="abstract"><p><%= sanitize( @page.abstract )%></p></div>
   <div id="headline_image"><%= headline_image %></div>
   <div class="body"><%= aggregate?(@page.body) %></div>
+  <%= render partial: 'content/asset_credits' %>
 </div>
 
 <%= will_paginate(@content_collection) if @content_collection %>
diff --git a/app/views/nodes/edit.html.erb b/app/views/nodes/edit.html.erb
index 25f15c2..2c1e975 100644
--- a/app/views/nodes/edit.html.erb
+++ b/app/views/nodes/edit.html.erb
@@ -82,11 +82,18 @@
           <ul id="related_asset_list" class="thumbnail_list">
             <% @page.related_assets.includes(:asset).each do |related| %>
               <li data-url="<%= node_related_asset_path(@node, related) %>"
+                  data-asset-id="<%= related.asset.id %>"
                   data-large-url="<%= related.asset.upload.url(:large) %>"
                   data-original-url="<%= related.asset.upload.url %>"
-                  data-name="<%= related.asset.name %>">
+                  data-name="<%= related.asset.name %>"
+                  data-headline="<%= related.headline? %>"
+                  class="<%= "is_headline" if related.headline? %>">
                 <span class="related_asset_handle"><%= icon("grip-vertical", library: "tabler", "aria-hidden": true) %></span>
                 <%= image_tag related.asset.upload.url(:thumb) %>
+                <button type="button" class="related_asset_set_headline"
+                        aria-pressed="<%= related.headline? %>" aria-label="Set as headline image">
+                  <%= icon("star", library: "tabler", "aria-hidden": true) %>
+                </button>
                 <button type="button" class="related_asset_remove" aria-label="Remove image">
                   <%= icon("x", library: "tabler", "aria-hidden": true) %>
                 </button>
@@ -102,6 +109,9 @@
         <li>
           <span class="related_asset_handle"><%= icon("grip-vertical", library: "tabler", "aria-hidden": true) %></span>
           <img src="">
+          <button type="button" class="related_asset_set_headline" aria-pressed="false" aria-label="Set as headline image">
+            <%= icon("star", library: "tabler", "aria-hidden": true) %>
+          </button>
           <button type="button" class="related_asset_remove" aria-label="Remove image">
             <%= icon("x", library: "tabler", "aria-hidden": true) %>
           </button>
diff --git a/config/asset_licenses.yml b/config/asset_licenses.yml
new file mode 100644
index 0000000..5cf377f
--- /dev/null
+++ b/config/asset_licenses.yml
@@ -0,0 +1,25 @@
+# config/asset_licenses.yml
+cc0:
+  url: "https://creativecommons.org/publicdomain/zero/1.0/"
+  requires_attribution: false
+  style: license
+cc_by_4:
+  url: "https://creativecommons.org/licenses/by/4.0/"
+  requires_attribution: true
+  style: license
+cc_by_sa_4:
+  url: "https://creativecommons.org/licenses/by-sa/4.0/"
+  requires_attribution: true
+  style: license
+public_domain:
+  url:
+  requires_attribution: false
+  style: note
+used_with_permission:
+  url:
+  requires_attribution: false
+  style: note
+own_work:
+  url:
+  requires_attribution: false
+  style: note
diff --git a/config/locales/de.yml b/config/locales/de.yml
index f64f6cd..21c8ebf 100644
--- a/config/locales/de.yml
+++ b/config/locales/de.yml
@@ -116,3 +116,17 @@ de:
     revision_created: "angelegt am %{date} von %{actor}"
     revision_published: "veröffentlicht am %{date} von %{actor}"
     revision_restored: "wiederhergestellt am %{date} von %{actor}"
+
+  open_gallery: "Gallerie anzeigen"
+  asset_licenses:
+    cc0: "CC0"
+    cc_by_4: "CC BY 4.0"
+    cc_by_sa_4: "CC BY-SA 4.0"
+    public_domain: "Gemeinfrei"
+    used_with_permission: "Mit Genehmigung verwendet"
+    own_work: "Eigenes Werk"
+
+  asset_credits:
+    photo: "Foto %{name}"
+    by: "von %{creator}"
+    licensed_under: "Lizenziert unter %{license}"
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8a8acc1..1afcf21 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -68,3 +68,17 @@ en:
     revision_created: "created %{date} by %{actor}"
     revision_published: "published %{date} by %{actor}"
     revision_restored: "restored %{date} by %{actor}"
+
+  open_gallery: "Open gallery"
+  asset_licenses:
+    cc0: "CC0"
+    cc_by_4: "CC BY 4.0"
+    cc_by_sa_4: "CC BY-SA 4.0"
+    public_domain: "Public domain"
+    used_with_permission: "Used with permission"
+    own_work: "Own work"
+
+  asset_credits:
+    photo: "Photo %{name}"
+    by: "by %{creator}"
+    licensed_under: "Licensed under %{license}"
diff --git a/db/migrate/20260720115941_add_credit_fields_to_assets.rb b/db/migrate/20260720115941_add_credit_fields_to_assets.rb
new file mode 100644
index 0000000..638d894
--- /dev/null
+++ b/db/migrate/20260720115941_add_credit_fields_to_assets.rb
@@ -0,0 +1,7 @@
+class AddCreditFieldsToAssets < ActiveRecord::Migration[8.1]
+  def change
+    add_column :assets, :license_key, :string
+    add_column :assets, :creator, :string
+    add_column :assets, :source_url, :string
+  end
+end
diff --git a/db/migrate/20260720120917_add_headline_to_related_assets.rb b/db/migrate/20260720120917_add_headline_to_related_assets.rb
new file mode 100644
index 0000000..c77e1ef
--- /dev/null
+++ b/db/migrate/20260720120917_add_headline_to_related_assets.rb
@@ -0,0 +1,7 @@
+class AddHeadlineToRelatedAssets < ActiveRecord::Migration[8.1]
+  def change
+    add_column :related_assets, :headline, :boolean, null: false, default: false
+    add_index :related_assets, :page_id, unique: true, where: "headline = true",
+               name: "index_related_assets_on_page_id_headline_uniqueness"
+  end
+end
diff --git a/lib/tasks/assets.rake b/lib/tasks/assets.rake
index 563dfad..9d4b048 100644
--- a/lib/tasks/assets.rake
+++ b/lib/tasks/assets.rake
@@ -16,4 +16,24 @@ namespace :assets do
       puts "Regenerated variants for Asset##{asset.id} (#{asset.name})"
     end
   end
+
+desc "One-shot: flag each live page's current first-by-position image as its headline"
+  task backfill_headline: :environment do
+    count = 0
+    page_ids = (Node.where.not(head_id: nil).pluck(:head_id) +
+                Node.where.not(draft_id: nil).pluck(:draft_id)).uniq
+
+    Page.where(id: page_ids).find_each do |page|
+      next if page.related_assets.where(headline: true).exists?
+
+      first_image = page.related_assets.joins(:asset).merge(Asset.images).order(:position).first
+      next unless first_image
+
+      first_image.update!(headline: true)
+      count += 1
+    end
+
+    puts "Flagged #{count} pages' current first image as headline."
+  end
+
 end
diff --git a/public/javascripts/admin_interface.js b/public/javascripts/admin_interface.js
index e9f96c2..7fb1dc2 100644
--- a/public/javascripts/admin_interface.js
+++ b/public/javascripts/admin_interface.js
@@ -277,10 +277,12 @@ cccms = {
 
       var items = $('#related_asset_list li').map(function() {
         return {
+          id: $(this).data('asset-id'),
           thumb: $(this).find('img').attr('src'),
           large: $(this).data('large-url'),
           original: $(this).data('original-url'),
-          name: $(this).data('name')
+          name: $(this).data('name'),
+          headline: $(this).data('headline') === true
         };
       }).get();
       cccms.inline_images.items = items;
@@ -293,7 +295,7 @@ cccms = {
         items.forEach(function(item, i) {
           var wrapper = $('<div class="inline_image_picker_item"></div>');
           wrapper.append($('<img>').attr('src', item.thumb).attr('data-index', i));
-          if (i === 0) {
+          if (item.headline) {
             wrapper.append($('<span>', { "class": "inline_image_picker_headline_badge" }).text("Headline"));
           }
           grid.append(wrapper);
@@ -317,8 +319,10 @@ cccms = {
         ? 'inline-image inline-image--full'
         : 'inline-image inline-image--half inline-image--' + placement;
 
-      var html = '<a href="' + item.original + '" class="glightbox" data-gallery="page-' + cccms.inline_images.node_id + '">' +
-                  '<img src="' + item.large + '" class="' + classes + '" alt="' + cccms.inline_images.escape_attr(item.name) + '"></a>';
+      var esc = cccms.inline_images.escape_attr;
+      var html = '<a href="' + esc(item.original) + '" class="glightbox" data-gallery="page-' + esc(cccms.inline_images.node_id) + '"' +
+                 ' data-title="' + esc(item.name) + '" data-description="#credit_for_asset_' + esc(item.id) + '">' +
+                 '<img src="' + esc(item.large) + '" class="' + classes + '" alt="' + esc(item.name) + '"></a>';
 
       cccms.inline_images.editor.insertContent(html);
       $('#inline_image_picker').hide();
diff --git a/public/javascripts/related_assets.js b/public/javascripts/related_assets.js
index 3340fa7..cc07d86 100644
--- a/public/javascripts/related_assets.js
+++ b/public/javascripts/related_assets.js
@@ -5,8 +5,6 @@ related_assets = {
     var createUrl = container.data("create-url");
     var list = $("#related_asset_list");
 
-    related_assets.update_headline_badge(list);
-
     initSearchPicker({
       inputSelector: "#related_asset_search_term",
       resultsSelector: "#related_asset_search_results",
@@ -44,7 +42,6 @@ related_assets = {
           url: ui.item.data("url"),
           data: "position=" + newPosition
         });
-        related_assets.update_headline_badge(list);
       }
     });
 
@@ -55,21 +52,29 @@ related_assets = {
         url: item.data("url"),
         success: function() {
           item.remove();
-          related_assets.update_headline_badge(list);
         }
       });
     });
-  },
 
-  update_headline_badge: function(list) {
-    list.find(".related_asset_headline_badge").remove();
-    var first = list.children("li").first();
-    if (first.length) {
-      $("<span>", {
-        "class": "related_asset_headline_badge",
-        "title": "Shown automatically as this page's headline image"
-      }).text("Headline").insertBefore(first.find(".related_asset_remove"));
-    }
+    list.on("click", ".related_asset_set_headline", function() {
+      var button = $(this);
+      var item = button.closest("li");
+      var makeHeadline = button.attr("aria-pressed") !== "true";
+
+      $.ajax({
+        type: "PATCH",
+        url: item.data("url"),
+        data: "headline=" + makeHeadline,
+        success: function() {
+          list.children("li").removeClass("is_headline")
+              .find(".related_asset_set_headline").attr("aria-pressed", "false");
+          if (makeHeadline) {
+            item.addClass("is_headline");
+            button.attr("aria-pressed", "true");
+          }
+        }
+      });
+    });
   },
 
   attach: function(assetId, createUrl, list) {
@@ -81,13 +86,13 @@ related_assets = {
       success: function(related) {
         var item = $($("#related_asset_template").html().trim());
         item.attr("data-url", related.url);
+        item.attr("data-asset-id", related.asset_id);
         item.attr("data-large-url", related.large_url);
         item.attr("data-original-url", related.original_url);
         item.attr("data-name", related.name);
         item.find("img").attr("src", related.thumb_url);
         list.append(item);
         list.sortable("refresh");
-        related_assets.update_headline_badge(list);
         $("#related_asset_search_term").val("");
         $("#related_asset_search_results").slideUp().empty();
       }
diff --git a/public/stylesheets/admin.css b/public/stylesheets/admin.css
index 0e11747..b171800 100644
--- a/public/stylesheets/admin.css
+++ b/public/stylesheets/admin.css
@@ -1327,15 +1327,6 @@ div#image_browser ul li {
   height: 1rem;
 }
 
-.related_asset_headline_badge {
-  background: #fff3cd;
-  color: #6b5900;
-  border-radius: 999px;
-  padding: 0.1rem 0.6rem;
-  font-size: 0.75em;
-  white-space: nowrap;
-}
-
 .related_asset_remove {
   display: flex;
   align-items: center;
@@ -1372,6 +1363,32 @@ div#image_browser ul li {
   border-radius: 4px;
 }
 
+.related_asset_set_headline {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: none;
+  border: none;
+  padding: 2px;
+  cursor: pointer;
+  color: #969696;
+} 
+
+.related_asset_set_headline svg {
+  width: 0.9rem;
+  height: 0.9rem;
+}
+
+.related_asset_set_headline:hover,
+.related_asset_set_headline[aria-pressed="true"] {
+  color: #6b5900;
+}
+
+.thumbnail_list li.is_headline {
+  border-color: #fff3cd;
+  background-color: #fffdf5;
+}
+
 /* ============================================================
    Live edit preview
    ============================================================ */
diff --git a/public/stylesheets/ccc.css b/public/stylesheets/ccc.css
index a07cc4d..8358d06 100644
--- a/public/stylesheets/ccc.css
+++ b/public/stylesheets/ccc.css
@@ -747,3 +747,11 @@ div.teaser_ruler {
   float: right;
   margin-left: 1rem;
 }
+
+#asset_credits .glightbox-desc {
+  display: none;
+}
+
+#asset_credits .headline_credit {
+  display: block;
+}
diff --git a/test/controllers/related_assets_controller_test.rb b/test/controllers/related_assets_controller_test.rb
index 9d20cbb..2384adc 100644
--- a/test/controllers/related_assets_controller_test.rb
+++ b/test/controllers/related_assets_controller_test.rb
@@ -88,4 +88,50 @@ class RelatedAssetsControllerTest < ActionController::TestCase
     ordered_asset_ids = node.draft.reload.related_assets.map(&:asset_id)
     assert_equal [second.id, first.id], ordered_asset_ids
   end
+
+  test "update sets the headline flag" do
+    login_as :quentin
+    node = Node.root.children.create!(:slug => "related_assets_headline_test")
+    asset = Asset.create!(:name => "headline-photo", :upload_content_type => "image/png")
+    node.draft.assets << asset
+    related = node.draft.related_assets.find_by(:asset_id => asset.id)
+
+    patch :update, params: { :node_id => node.id, :id => related.id, :headline => "true" }
+
+    assert_response :success
+    assert related.reload.headline?
+  end
+
+  test "update with headline=true clears any previous headline on the same page" do
+    login_as :quentin
+    node = Node.root.children.create!(:slug => "related_assets_headline_swap_test")
+    first  = Asset.create!(:name => "first-headline", :upload_content_type => "image/png")
+    second = Asset.create!(:name => "second-headline", :upload_content_type => "image/png")
+    node.draft.assets << first
+    node.draft.assets << second
+
+    first_related  = node.draft.related_assets.find_by(:asset_id => first.id)
+    second_related = node.draft.related_assets.find_by(:asset_id => second.id)
+    first_related.update!(:headline => true)
+
+    patch :update, params: { :node_id => node.id, :id => second_related.id, :headline => "true" }
+
+    assert_response :success
+    assert_not first_related.reload.headline?
+    assert second_related.reload.headline?
+  end
+
+  test "update with headline=false clears the headline" do
+    login_as :quentin
+    node = Node.root.children.create!(:slug => "related_assets_headline_unset_test")
+    asset = Asset.create!(:name => "unset-headline", :upload_content_type => "image/png")
+    node.draft.assets << asset
+    related = node.draft.related_assets.find_by(:asset_id => asset.id)
+    related.update!(:headline => true)
+
+    patch :update, params: { :node_id => node.id, :id => related.id, :headline => "false" }
+
+    assert_response :success
+    assert_not related.reload.headline?
+  end
 end
diff --git a/test/models/asset_license_test.rb b/test/models/asset_license_test.rb
new file mode 100644
index 0000000..9f2d04f
--- /dev/null
+++ b/test/models/asset_license_test.rb
@@ -0,0 +1,31 @@
+require 'test_helper'
+
+class AssetLicenseTest < ActiveSupport::TestCase
+  test "find returns a populated entry for a known key" do
+    entry = AssetLicense.find("cc_by_4")
+
+    assert_equal "cc_by_4", entry.key
+    assert_equal "https://creativecommons.org/licenses/by/4.0/", entry.url
+    assert entry.requires_attribution
+    assert_equal "license", entry.style
+  end
+
+  test "find returns nil for an unknown or blank key" do
+    assert_nil AssetLicense.find("not_a_real_license")
+    assert_nil AssetLicense.find(nil)
+    assert_nil AssetLicense.find("")
+  end
+
+  test "keys includes every dictionary entry" do
+    assert_includes AssetLicense.keys, "cc0"
+    assert_includes AssetLicense.keys, "own_work"
+  end
+
+  test "a note-style entry has no attribution requirement and no url" do
+    entry = AssetLicense.find("own_work")
+
+    assert_not entry.requires_attribution
+    assert_nil entry.url
+    assert_equal "note", entry.style
+  end
+end
diff --git a/test/models/asset_test.rb b/test/models/asset_test.rb
index a1041e4..d246abe 100644
--- a/test/models/asset_test.rb
+++ b/test/models/asset_test.rb
@@ -19,5 +19,26 @@ class AssetTest < ActiveSupport::TestCase
     assert_equal 0, draft.assets.length
     assert_equal 0, RelatedAsset.count
   end
-  
+
+  test "image? is true for supported image content types" do
+    assert Asset.new(:upload_content_type => "image/png").image?
+    assert Asset.new(:upload_content_type => "image/jpeg").image?
+  end
+
+  test "image? is false for non-image content types" do
+    assert_not Asset.new(:upload_content_type => "application/pdf").image?
+    assert_not Asset.new(:upload_content_type => nil).image?
+  end
+
+  test "license_key must be a known dictionary key" do
+    asset = Asset.new(:license_key => "not_a_real_license")
+    I18n.with_locale(:en) do
+      assert_not asset.valid?
+      assert_includes asset.errors[:license_key], "is not included in the list"
+    end
+  end
+
+  test "license_key may be blank" do
+    assert Asset.new(:license_key => nil).valid?
+  end  
 end
diff --git a/test/models/helpers/content_helper_test.rb b/test/models/helpers/content_helper_test.rb
index a7ed478..d6c7b43 100644
--- a/test/models/helpers/content_helper_test.rb
+++ b/test/models/helpers/content_helper_test.rb
@@ -2,7 +2,81 @@ require 'test_helper'
 
 class ContentHelperTest < ActionView::TestCase
   test "weekday_abbr delegates through the current I18n locale" do
-    I18n.locale = :de
-    assert_equal "Mo", weekday_abbr(Time.parse("2026-07-06"))
+    I18n.with_locale(:de) do
+      assert_equal "Mo", weekday_abbr(Time.parse("2026-07-06"))
+    end
+  end
+
+  test "asset_credit returns nil for a nil asset" do
+    assert_nil asset_credit(nil)
+  end
+
+  test "asset_credit returns nil when creator, source, and license are all blank" do
+    assert_nil asset_credit(Asset.new(:name => "blank"))
+  end
+
+  test "asset_credit renders creator, source link, and license link when all are present" do
+    asset = Asset.new(:name => "demo", :creator => "Jane Doe",
+                       :source_url => "https://example.org/photo", :license_key => "cc_by_4")
+
+    result = I18n.with_locale(:en) { asset_credit(asset) }
+
+    assert_match %r{<a href="https://example.org/photo">Photo demo</a>}, result
+    assert_match "by Jane Doe", result
+    assert_match %r{<a href="https://creativecommons.org/licenses/by/4.0/">Licensed under CC BY 4.0</a>}, result
+  end
+
+  test "asset_credit falls back to plain text when source_url is blank" do
+    asset = Asset.new(:name => "demo", :creator => "Jane Doe", :license_key => "cc_by_4")
+    assert_no_match %r{<a href="[^"]*">Photo demo</a>}, I18n.with_locale(:en) { asset_credit(asset) }
+  end
+
+  test "asset_credit omits the 'by' clause when creator is blank" do
+    asset = Asset.new(:name => "demo", :source_url => "https://example.org/photo", :license_key => "cc_by_4")
+    assert_no_match "by ", I18n.with_locale(:en) { asset_credit(asset) }
+  end
+
+  test "a note-style license renders with no 'Licensed under' prefix and no link" do
+    asset = Asset.new(:name => "demo", :creator => "CCC", :license_key => "own_work")
+    result = I18n.with_locale(:en) { asset_credit(asset) }
+
+    assert_match "Own work", result
+    assert_no_match "Licensed under", result
+    assert_no_match "<a", result
+  end
+
+  test "asset_credit degrades gracefully when the license_key is no longer in the dictionary" do
+    asset = Asset.new(:name => "demo", :creator => "Jane Doe")
+    asset.license_key = "a_retired_key"
+
+    result = I18n.with_locale(:en) { asset_credit(asset) }
+
+    assert_match "Photo demo by Jane Doe", result
+    assert_no_match "Licensed under", result
+  end
+
+  test "headline_image renders nothing when no images are attached" do
+    node = Node.root.children.create!(:slug => "headline_image_empty_test")
+    @page = node.draft
+    assert_nil headline_image
+  end
+
+  test "headline_image renders the flagged headline asset" do
+    node = Node.root.children.create!(:slug => "headline_image_flagged_test")
+    asset = Asset.create!(:name => "flagged", :upload_content_type => "image/png")
+    node.draft.assets << asset
+    node.draft.related_assets.find_by(:asset_id => asset.id).update!(:headline => true)
+    @page = node.draft
+
+    assert_match "glightbox", headline_image
+  end
+
+  test "headline_image falls back to a gallery-open caption when no headline is flagged" do
+    node = Node.root.children.create!(:slug => "headline_image_no_flag_test")
+    asset = Asset.create!(:name => "unflagged", :upload_content_type => "image/png")
+    node.draft.assets << asset
+    @page = node.draft
+
+    I18n.with_locale(:en) { assert_match t(:open_gallery), headline_image }
   end
 end
diff --git a/test/models/related_asset_test.rb b/test/models/related_asset_test.rb
index a739e6b..710b4cc 100644
--- a/test/models/related_asset_test.rb
+++ b/test/models/related_asset_test.rb
@@ -1,8 +1,44 @@
 require 'test_helper'
 
-class RelatedImageTest < ActiveSupport::TestCase
-  # Replace this with your real tests.
-  test "the truth" do
-    assert true
+class RelatedAssetTest < ActiveSupport::TestCase
+  test "headline can be set on an image asset" do
+    node = Node.root.children.create!(:slug => "related_asset_headline_image_test")
+    asset = Asset.create!(:name => "photo", :upload_content_type => "image/png")
+    node.draft.assets << asset
+    related = node.draft.related_assets.find_by(:asset_id => asset.id)
+
+    related.headline = true
+    assert related.valid?
+  end
+
+  test "headline cannot be set on a non-image asset" do
+    node = Node.root.children.create!(:slug => "related_asset_headline_pdf_test")
+    asset = Asset.create!(:name => "programme", :upload_content_type => "application/pdf")
+    node.draft.assets << asset
+    related = node.draft.related_assets.find_by(:asset_id => asset.id)
+
+    related.headline = true
+    assert_not related.valid?
+    assert_includes related.errors[:headline], "can only be set on image assets"
+  end
+
+  test "the headline validation does not raise when asset is missing" do
+    related = RelatedAsset.new(:headline => true)
+    assert_not related.valid?
+  end
+
+  test "at most one headline per page is enforced at the database level" do
+    node = Node.root.children.create!(:slug => "related_asset_headline_uniqueness_test")
+    first  = Asset.create!(:name => "first", :upload_content_type => "image/png")
+    second = Asset.create!(:name => "second", :upload_content_type => "image/png")
+    node.draft.assets << first
+    node.draft.assets << second
+
+    node.draft.related_assets.find_by(:asset_id => first.id).update!(:headline => true)
+    second_related = node.draft.related_assets.find_by(:asset_id => second.id)
+
+    assert_raises(ActiveRecord::RecordNotUnique) do
+      RelatedAsset.where(:id => second_related.id).update_all(:headline => true)
+    end
   end
 end