Add site setting for domains to never download images from

app/jobs/regular/pull_hotlinked_images.rb

@@ -87,7 +87,8 @@ module Jobs
     def is_valid_image_url(src)
       src.present? &&
       !Discourse.store.has_been_uploaded?(src) &&
-      !src.start_with?(Discourse.asset_host || Discourse.base_url_no_prefix)
+      !src.start_with?(Discourse.asset_host || Discourse.base_url_no_prefix) &&
+      SiteSetting.should_download_images?(src)
     end
 
   end

app/models/site_setting.rb

@@ -72,6 +72,16 @@ class SiteSetting < ActiveRecord::Base
                   .first
   end
 
+  def self.should_download_images?(src)
+    setting = disabled_image_download_domains
+    return true unless setting.present?
+    host = URI.parse(src).host
+
+    return !(setting.split('|').include?(host))
+  rescue URI::InvalidURIError
+    return true
+  end
+
   def self.scheme
     use_https? ? "https" : "http"
   end

config/locales/server.en.yml

@@ -605,6 +605,7 @@ en:
     crawl_images: "Enable retrieving images from third party sources to insert width and height dimensions"
     download_remote_images_to_local: "Download a copy of remote images hotlinked in posts"
     download_remote_images_threshold: "Amount of minimum available disk space required to download remote images locally (in percent)"
+    disabled_image_download_domains: "A pipe-delimited list of domains from which linked images will never be downloaded."
     ninja_edit_window: "Number of seconds after posting where edits do not create a new version"
     post_edit_time_limit: "Amount of time in minutes in which posts can be edited and deleted by the author. Set to 0 to allow editing and deleting posts at any time."
     edit_history_visible_to_public: "Allow everyone to see previous versions of an edited post. When disabled, only staff members can view edit history."

config/site_settings.yml

@@ -302,6 +302,9 @@ files:
       test: false
       default: true
   download_remote_images_threshold: 20
+  disabled_image_download_domains:
+    list: true
+    default: ''
   create_thumbnails: true
   clean_up_uploads: false
   clean_orphan_uploads_grace_period_hours: 1