Digital Fingerprinting

Looking for someone that has knowledge and can implement digital finger printing on pictures and videos Meaning that any time a (paid member) downloads a video or a picture (or a zip of pictures) a serial number relating to that member is injected into the video or picture. The purpose is to find out who is signing up to my website as a paid member and pirating my work. The payment/protection system I use is [login to view URL] - the fingerprinting will also have to work for amember remote.