A few ways, its up to you, all that matters is they dont know where it is so they cant remove it. For video DVD's you could put a image with there name on one of the video frames before encoding it, and saving the frame number so you can check it if you get hold of a illegal copy, or you could use IfoEdit to set the Provider ID to the persons name, or you could use a hex editor too add there name at the end of one of the vob files. I would go with the first one, as it would be very hard to spot without checking through every single video frame, and re-encoding wont remove it like it will for the other two.
Ben
