I have a PHP website where people can fill out help-tickets. It allows them to upload screenshots for their ticket. I allow gif, psd, bmp, jpg, png, tif to be uploaded. Upon
I dont know much about image formats, but recreating the images and then storing the result, I feel has a good chance of eliminating unnecessary tricky stuff. Especially if you strip all the meta data like comments and all the other types of optional embedded fields that some image formats support.