When I was about 25 I noticed that a 2D photo appeared 3D when looked at through a magnifying glass. First I thought it depended on the lens, but then realized it was because I looked at the picture by just one eye - exactly as the camera lens had seen it in reality. I.e. there is much 3D information in the picture, but discarded as 3D when both eyes simultaneously (unconsciously) judge it as 2D. I showed this to some friends and almost all of them agreed I was right. Most of them also thought my explanation for this "phenomenon" was reasonable. Although it didn´t work for everyone. But it is not a faint farfetched illusion - rather surprising and to some people even scaring. But first after a moment of perhaps 10 - 20 sec the 2D picture "jumps" into 3D.