Even though this was accepted in the original PR, it's something that has been nagging me.  I'm not sure that we should say `#is_a_digital_image?` because we may begin to get objects that are not images that we'll want to display image behaviors.  In the item_level_merge branch of the old SearchWorks codebase has renamed this method as `#has_image_behavior?`.  Perhaps we can rename this method to something more generic that indicates that we're identifying a particular behavior and not an item type.