1) We capture two face images and check for changes and natural motion. A 3D face moves differently from a 2D photo, and our sophisticated motion-analysis algorithms detect this difference. 2) We detect video replays and other copies like an avatar with a special texture-based algorithm that knows when a recaptured version of a person is presented instead of a real person. 3) Optionally, we can guide the user to turn their head a certain way and verify that the head was turned in the specified direction (challenge-response).