Repeating patterns embedded in screenshots taken with WoW's game client application can be decrypted to identify you, a report on Slashdot suggests. Posters on the OwnedCore forum claim that the watermark can be decoded to reveal user IDs, the time the screenshot was captured and the IP address of the server.
"A few days ago I noticed some weird artifacts covering the screenshots I captured using the WoW game client application," says Slashdot poster kgkoutzis. "I sharpened the images and found a repeating pattern secretly embedded inside. I posted this information on the OwnedCore forum and after an amazing three-day cooperation marathon, we managed to prove that all our WoW screenshots, since at least 2008, contain a custom watermark."
We've tried this, following the instructions on the OwnedCore forum, and our screenshots do indeed contain a repeating pattern which was not replicated in thirdparty screenshot apps. There may be plausible reasons for Acti-Blizz doing this: the watermark could be used to track down players who are running private servers, or otherwise breaking the terms of service, and have been silly enough to take a picture of their infringing activity. But the concern is that broadcasting user IDs may leave players open to stalking, griefing and phishing scams.
Setting the quality to the highest possible quality removes the watermark - perhaps because it would be too visible on screenshots of this high quality. You can change your screenshots to this setting by typing: /console SET screenshotQuality "10"
Should you be feeling paranoid enough to purge your screenshots from the web, it seems that the watermarking was introduced after the Wrath of the Lich King - and, coincidently, after the Activision-Blizzard merger.
We've reached out to the company for confirmation and comment.
The terms of service do account for the sharing of such information, of course, but what do you reckon? Do you have a reasonable expectation that this information be kept private?