add img_description for front-end

app/controllers/announcements_controller.rb

@@ -340,6 +340,7 @@ class AnnouncementsController < ApplicationController
     img_src = nil
     subtitle_ann = announcement.subtitle if announcement.display_subtitle?
     img_src = (announcement.image.thumb.url || "/assets/announcement-default.jpg") if announcement.display_img?
+    img_description = announcement.image_description if announcement.image_description.present?
 
     {
       "tags" => tags,
@@ -353,6 +354,7 @@ class AnnouncementsController < ApplicationController
         "body" =>announcement.text,
         "image" => announcement.image.url,
         "img_src" => img_src,
+        "img_description" => img_description,
         "alt_title" => desc
       },
       "impressionist" => (announcement.is_preview ? nil : announcement),