I'm moderating a closed section of a forum - think 'covered by NDA' (not actually, but it's a good equivalent of the situation), with restricted access.
Sometimes we find screenshots from that forum posted by some rogue user anonymously in places where they definitely shouldn't appear. And the screenshots being anonymous, with no discernable features, don't let us find the rogue and draw consequences.
I'd like to learn of some way to affect page appearance so that a screenshot of it could be traced to the author of the screenshot - maybe some kind of steganography that can survive lightweight compression, or other inconspicious elements that would allow to identify, whose account these screenshots were made from? Specifically, possible to appear broadly enough that even a relatively small part of the screen (say, one post) is sufficient to identify the culprit?
I tried "cooking my own" embedding something akin to low-contrast barcode in borders around posts, but it was neither inconspicious enough nor durable enough to survive 85% quality JPEG compression.