The only complaint I am getting is from VERY frustrated users who try to upload their images over and over (after they have resized them to fit the requirements, for instance) and then it says “Image already exists.” You would think people would know to just re-name the image themselves, but they don’t.
It would be AWESOME if you could allow them to upload images with the same name some how. At the very least, could you modify the error message to ask them to try renaming the image?