Include Riyad Preukschas suggestions.

app/helpers/application_helper.rb

@@ -160,7 +160,8 @@ module ApplicationHelper
   end
 
   def image_url(source)
-    root_url.sub(/#{root_path}$/,'') + path_to_image(source)
+    # prevent relative_root_path being added twice (it's part of root_url and path_to_image)
+    root_url.sub(/#{root_path}$/, path_to_image(source))
   end
   alias_method :url_to_image, :image_url
 end