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Imagine a photo that is taken of someone looking straight at the camera.

Why when we look at the photo now from any direction it looks as if the person is looking straight at us?

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3 Answers

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Because the person is looking straight at you. When you look at a face in three dimensions, there are a number of visual effects that indicate to your brain that the object is rotating. For a rotating complex object like a human head, the primary indicator is closer objects covering those farther away. If a person who is facing you, turns to their right, their nose will cover part of their right cheek from your perspective.

When you take a photograph of the person from straight on, their nose will never cover part of their cheek; a person viewing the photograph from any angle (except the back) will always see the subject's entire face as though you were looking straight on.

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I do not think the nose has anything to do with it. I am talking about the eyes, the eyes themselves are looking at you regardless of the angle from which you are looking at the photo. I can cover the nose and will get the same effect. – Revo Jul 30 '12 at 23:48
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I note gun in movie poster ... no matter through angle which I look ... it always looks it it's going to shoot me :D – experimentX Jul 30 '12 at 23:58
Revo, I was just using the nose as an example because it is very prominent. Yes, you will have the same effect if you cover the nose because everything I said about the nose is also true of the eyebrows, and the eyelashes, and the left side of the eye, and the lips, and the cheeks, etc. It is not a matter of the nose looking like it does, it is a matter of no feature on the face ever being covered by any other. The effect is called foreshortening... a photo does not have it. – AdamRedwine Jul 31 '12 at 1:28
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You mean this effect?

http://media.uniklinik-freiburg.de/aug/homede/mit/bach/mdia/rotating-facemask.ogg

Because all your ancestors that didn't immediately recognise a human (or primate) face didn't get suckled and didn't grow up to be ancestors.

It doesn't just need a face, pretty much any shaded 3D convex shape can appear to be concave (ie curved outward like a face) from this effect. We have this problem in presenting 3D scans of things like oil basins - a proportion of people can only see it as convex.

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Eyes are 2D flat circles, instead of spheres. From an angle, the pupil is still in the center for the circle, but gets shifted off-center for the sphere. It's subtle, but your brain is sensitive for this.

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by the way, for the gun (which is a better example I think), change sphere to cylinder above – bobuhito Jul 31 '12 at 16:37

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