Switched enum to explicit ints so that we can be sure of a stable value. Added a convenience getter for just the image resources.
Switched from URLs to Strings. The most satisfactory explanation being: maybe the user enters a malformed URL but a human at the other end can figure it out?
Invented a sort-of namespace and made these static; moved them to a move relevant location.
Made an attempt to introduce three image resources in the default scaffolding.