Sleuths in the Ownedcore forums have uncovered what appears to be a secret watermarking scheme built into World of Warcraft's screenshot function. Screenshots captured within the game are reportedly stamped with digital watermarks revealing the player's account ID, a time stamp, and information about the realm, including its IP address. Some are arguing that the supposed watermarks are nothing more than compression artifacts, but reading deeper into the forum thread reveals snippets of code that seem to confirm the data being embedded in screenshots.
The watermarking has apparently been going on since at least 2010, and it may be easy to circumvent. Simply typing: /console SET screenshotQuality "10" is supposed to disable the watermarks entirely.
According to one forum poster, a suspected Blizzard employee, the watermarks are there to track leaks. Testers get early access to WoW content, and Blizzard doesn't want them sharing it with the public. The information stored in the watermarks would seem to be sufficient to track down unauthorized leaks. The realm IP should also help Blizzard sniff out private servers, which are forbidden.
There's some predictable outcry about what Blizzard is doing, but it's hard to get too worked up about this being some kind of reprehensible privacy violation. The only user data is the account ID, which seems pretty innocuous to me. Time stamps are hardly harmful, and realm information could only prove troublesome if you're playing on unauthorized servers. The World of Warcraft terms of service appear to allow this sort of information to be communicated to Blizzard, as well.