Added image_url method for Screenshot model

app/models/screenshot.rb

@@ -0,0 +1,10 @@
+class Screenshot < ActiveRecord::Base
+  belongs_to :package
+
+  # Return the URL to this screenshot.
+  # size: 'small' (thumbnail) or 'large' (full-size)
+  # (If possible serve the screenshots statically from the web server.)
+  def image_url(size)
+    "/screenshots/#{self.package.name[0]}/#{self.package.name}/#{self.id}_#{size}.png"
+  end
+end