I have seen lots of stunning cakes on here with photos that are to dark, cake to far away, or the picture isn't sharp enough to see the details of the cake. I have been using Photoscape for several years now and its FREE on download.com from cnet.
You can also find it by going to: download.com and search for Photoscape.
You can do all kinds of things with color, brightness, sharpen, crop even enlarge a small photo (love this feature. Some of them I don't even know what they do because there are so many options.
Just thought this might help someone!