It cannot :( as it lacks a Camera. There may be 3rd Party models that include one, but the one from Google does not have this capability. I attached a photo of mine, pardon the grainyness, but at the top you can see a small oval, this is an Ambient Light sensor to adjust the screen brightness. There's 2 mics flanking the Sensor to it's sides.
I imagine in the next revision we may get a Camera though.