I can understand their motivation in wanting to catch hackers who posted screenshots to websites and whatnot. That said, it seems like a big security risk to attach the account info to something that's posted publicly. I'm sure there is a general ToS clause that covers their ass but it still seems pretty dumb.
Apparently you can defeat it by using a different screenshot quality or compression method.
Playing: Bloodborne, Pillars of Eternity, DOTA2 Watching: Vikings, Dig, The Jinx