module ActionView::Helpers::AssetUrlHelper

image_url "edit.png", host: "http://stage.example.com" # => http://stage.example.com/assets/edit.png

options is set, it overwrites global +config.action_controller.asset_host+ setting.
Since +image_url+ is based on +asset_url+ method you can set +:host+ options. If +:host+
This will use +image_path+ internally, so most of their behaviors will be the same.
Computes the full URL to an image asset.

def image_url(source, options = {})
  url_to_asset(source, { type: :image }.merge!(options))
end