Web content screen capture copy-protection

I have some sensitive content that I am presenting to authenticated users over the web, in a browser. I am looking for techniques which would allow me trace a screen shot or photograph of content back to a specific user by embedding identifying information in the web page.

The simplest approach would be placing the identifier in plain view, but this method isn't tamper resistant.

This lead me to think about steganography on the web.

Techniques like LSB embedding only work with images. It also wouldn't work well with poor-quality image capture, as is often the case camera phones.

Two example techniques I found are:

• Coded Anti-Piracy (used in film)
• Bacon's cipher

Are there similar techniques (or even libraries) which have been used on web content?

For the purposes of this question, I am not concerned with copy-prevention.