If they are tagged as Pixel perfect duplicate, it's a Bot who did that, which was programmed by nonamethanks. The Bit checks if images are pixel perfect, so you can assume that it is just a dupe and not of higher quality. Filesize doesn't determine if an image is of higher quality or not.
If you use the upload bookmarklet it'll check for similar images automatically before you submit the upload. If the filesize/resolution are nearly identical, there's a good chance they're pixel-perfect duplicates and you should avoid them.
