he's looking for "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…