Sound the news-horn! Sound it from the highest mountains! Ready your loins! Thief is back.
Unconfirmed leak, yada yada, you know the drill. But, yes, this very much appears to be screenshots of Square-Enix's rebooted Thief series and OHMIGOD THIS IS REALLY HAPPENING.
Update: now confirmed as real, called 'Thief', out on PC and next-gen consoleboxes in 2014.