note jimt <p>I might be more concerned about false negative matches, but it depends upon what the OP meant by comparing images. You could upload a jpeg of a dog that gets an MD5sum of 00000 (or whatever). I could upload a png of that same photo and that gets an M5sum of ABDEF. Someone else could come along an upload another jpeg at a slightly different compression setting and get an MD5sum of A188F.</p> <p>They're all different files, but they all represent the same image. To try and compensate for that, it'd require a more advanced technique like one of the articles linked to later on here in the thread to actually compare upon how the image actually looks, not merely how it's stored.</p> <p>Of course, if you just want to make sure the same file isn't uploaded twice, the md5sum should do just fine.</p> 586173 586174