How to recognize a person in front of a camera or a picture?

Question

CCTV

How is it understood that there is a human head in front of the camera (or two cameras), and not a drawing with a human head?

Answer 1

At least 2 ways:
1. Recognize by a 3D image (generated from a stereopair or an infrared 3D sensor)
2. Recognize in the infrared spectrum. In it, either the photo will not be visible at all, or the image will differ significantly from what is on the color camera.

Answer 2

From personal experience with cameras. If the IR illumination is taken out at a distance of about 20 cm from the lens, characteristic shadows from all protruding parts will appear on the face. A photo of such shadows will not give. Probably only relevant for embedded systems. Cheap and cheerful)

Answer 3

For authenticity, you can use fingerprint scanners, among them there are just models that distinguish a picture from a real hand.