Often the contest instigator asks for a description of the submitted image.
Even more often, I submit the same image to different contests (of course, if it's applicable to the contest in some way).
Some of my images have a meaningful description (at least to me), some not. In either case, many contests may deserve a variation of the original comment, but that would mean for the contestant changing it twice for any given contest. Even more troubling is the fact, that if you changed the image description (as it is implemented now) for one contest, it might make it inappropriate for another simultaneous contest.
provide an additional caption for each image contest submission, linked specifically to that image and that particular contest.
While I realize, that this request wouldn't be a high priority consideration in the FAA programming to-do-list, more descriptive (and sometimes more humorous) comments would increase the viewing pleasure and conceivably also the page visits and FAA ranking.