Lemme think. A camera that observes the room from the portrait, anyone that walks in is a dot on a plane, and it points the eye at the point on the plane. Should be doable. Yes, the Pi should handle that fairly easily.

The part that you'll have to figure out is making the eye ball rotate. There are GPIO pins on the Pi, so you can get the commands out, but you'll need to build the eyeball component yourself.