Obviously you first check if a human is looking at the screen. Apple had a patent application a few years back for that purpose... the camera operates in low power mode, simply looking for an orange blob (it turns out that all humans are a shade of orange... not pink or brown). When it sees the blob, it kicks into higher power mode to check the face. Samsung already had a feature to keep the power on if you were looking at the phone. Sounds like a derivation of that.
3/4/13 at 5:06pm