I HAVE AN IDEA
I think this all stems from a bad user interface.
Currently, users have to click on the image to go see the image description page. Many users do not know that. Proof: on OTRS we get tons of people who assume that the only resolution they can get is the thumbnail, and they ask for a larger version.
I can therefore understand that photographers want credits under the picture, since most users don't even know that they can get the credits by clicking.
Maybe MediaWiki should: - extract credits from the image description and show them as a tooltip over the image - or put a discreet link underneath for the informations (the small "enlarge this" icon we use at the right of the caption is NOT understood by most people).