[pa7]

that reminds me of another technique I used but didn't describe in the article which could be interesting for you:

encode the viewer's IP into the image (with steganography, wrote a small script for that) on the server (every request). whenever your image pops up somewhere in the web you know which IP address is to "blame" (easily bypassed with IP obfusication software though :) )

[scrollaway]

This is a commonly used technique in game alphas under NDAs (TESO and WoW WLK are the most recent example that come to my mind). The player's account information are embedded in the exif of the screenshots. If a screenshot leaks from someone who doesn't know better, it's possible to track it down.

[Malstrond]

>exif

WoW does much more than that: http://www.ownedcore.com/forums/world-of-warcraft/world-of-w...

[unsquare]

I've though about it, but there's a privacy concern that turns me off, it's the equivalent of having exif data in pictures, it's really great, until someone decides to do something questionable with the embedded data.