It's not a moving pic. However, our brains are tricking us into believing it is. If you stare into it, you'll see one or more of the circles moving, but when you direct your gaze directly on said circle, it stops moving and the other ones start.
for me if I focus on it all of it stops. Just focus on the middle row and you will see that if you focus on one of them it will stop moving. If you move your eyes one way they will move that way and vice versa.