Consider adding before/after image support
Many times photographers display "before" and "after" versions of images, for various reasons. Currently, they are limited to using animated GIFs, which is a suboptimal solution. I just saw a real neat implementation of a single-image-with-a-slider that you slide to see the before and after in a single image. Look at this article that illustrates how various U.S. landmarks will look after the sea level has risen several feet (because of global warming)
I'll bet that this would be real popular in the Retouching forum.