Why it seems that a man with a portrait looks right on you?
"Mona Lisa" Leonardo da Vinci is known not only to his mysterious smile. From any point of the hall it seems that her look is facing right on you. It is typical for most other portraits.
In fact, there is no mysticism. We are accustomed to the fact that a person looks at the interlocutor, if his pupils are facing. But in the reality of the eye three-dimensional. Consequently, the pupil can be seen in the profile, and in three quarters. And the image in the picture is flat, two-dimensional. However, the viewer and the portrait seeks to transfer the perception of a three-dimensional object. When the pupils are directed directly to you, you will seem at any angle that the hero of the picture turns after you.
Light, shadow and perspective are to blame. In the picture, they do not change, and therefore, if a person is drawn looking at you, he will remain so even when you change the location. Ultimately, the whole depth, created by the perspective, light and shadow, is a trick, an optical illusion that creates other illusions, including the view, the "tracking" for you.
But not all portraits. Only those where a person is depicted in Afas, that is, turned to the viewer. With a slightly unfolded head, the illusion will be incomplete. Going to the side, in which turned the depicted, most likely, you lose your opinion.