Hi, some people can hack the image size, especially gif images, I don’t know what they hack exactly, some say that they hack the image header or something like that, for example, most discussion forums set a max-size for avatars (say 65x65), now some people managed to upload bigger images (say 150x150) and it works because the image is detected as if it was 65x65 only, my question is how could they do that?

Thanks in advance.