The Last Guardian creator Fumito Ueda might be teasing something big.
During the development of The Last Guardian, Ueda left Sony's internal Team Ico division to head an independent studio, GenDESIGN, while working freelance on Guardian. It's at the new studio that the mysterious image first appeared.
You won't find the image at the main GenDESIGN webpage though. Instead you'll have to scroll down past the three birds at the GenDESIGN entrance page to actually see the teaser image. And what a tease it is.
The image depicts a pitch black setting illuminated solely by a mysterious figure sitting on a kind of raised platform. In front of the figure/source of light is what looks to be the body of a giant. It kind of looks vaguely humanoid but it's hard to tell. It kind of also looks like a claw.
Either way, the new teaser image fits very well with Ueda's M.O. of tiny person, large monster-thing. Whether this game will also take close to a decade to finish remains to be seen.
In the meantime, Team Ico fans can look forward to the upcoming Shadow of the Colossus remake for PS4 coming out in February.