I've always wondered if jpeg encoders added something like this to screenshots. Should be possible to add a compression-resilient pattern that encodes the screenshotter's host details.
Blizzard watermarks screenshots produced by World of Warcraft find and track users of emulated servers by embedding user account info and server IP all across the image.
I am, yes. But this was not the case when I played WoW 15 years ago. I mean, I knew that I was playing on a server, and of course they are tracking everything on a server. But for some reason this steganography in the screenshots just gets under my skin.
With current games I go in with the assumption that I'm in a public place, and act accordingly. But back then I really counted on my Personal Computer being personal, so this feels like a breach of trust.
I'm much less bothered by the idea of developers having access to things like aggregated anonymous heat maps, and more worried by the amount of individual details required to generate such a heat map.
I'm not sure about jpeg, but with an algorithm like 'deflate' the encoder is constantly making decisions about whether it's more efficient to represent a series of bytes as a literal or as a reference to a previous series. I think a steganographer could take advantage of that by encoding something like a tracking number in the form of the occasional less efficient decision.
