Illusion
Ever heard of Julian Beever?He's an English artist famous in Europe for his pavement art. What's so special about his art is that he drew it in complete distorted form, meant to be viewed only from a certain direction and angle... which would transform the flat 2-dimensional image into amazing 3D.
Here are some:
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But, if you view it from a 'wrong' direction and angle... it looks very odd, like this one:
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which suppose to look like this (from the right spot/angle):
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More....
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Great eh?