Host::Managed has a search defined for image names:

scoped_search :relation => :image, :on => :name, :complete_value => true

But it's only accessible with free text search by searching for just the image name. It should be possible to search specifically for image = foo as well.

Currently this definition registers the search field name (from :on) rather than an alias such as image or image_name. As name is used by host.name, no new field name is added for it.