"Art images should be GIF or JPG format only. The full image should be between 100 x 100 and 4000 x 4000 pixels and be less than 512 KB in size. The thumbnail image (if supplied) should be between 50 x 50 and 200 x 200 pixels and be less than 15 kb in size." I wanted to use a psd but the gallery here doesn't support it. So if I want to use a non-square shape I have to use a gif file.