There is a way to code all images so that you can track images on the web, its expensive but works well its available or used to be from a company called BayTSP their site is
http://www.baytsp.com/
This is not DIGIMARK which can be made unreadable in Photoshop. This is code that is placed in the image and you would need to know exactly where to be able to remove it.
I know it works because we have used it and a number of sites we deal with use it. But its expensive.
Cindy xx
