embed identification in file and resistance to detection

Question

Say I'm distributing a file that I want to be secret, and I assign each person that I give the file a unique id.

How can I embed this id in the file so that I can determine who leaks my file?

Some file formats have a section in which I can put information that won't render the file corrupt. But this is easily detectable by looking at the specific section, or by changing the information.

I would guess that any solution is identifiable by byte comparison, but I was wondering if there exists solutions that embed the id in a part that if changed, renders the file corrupt. (I would guess this would be file format specific, but this question is to learn about techniques, so I'd gladly read about specific cases.)

Thanks!

Answer 1

For image files and Unicode text you may use Steganography .

For audio files there are special watermarking algorithms that add noise not heard by humans.

You may use metadata to add watermarks, but they can be easily removed by end user.

See at what is currently possible in this SO question: Good library for Digital watermarking