This is a famous optical illusion, known as the '13 hidden faces'. It is also an attractive piece of art. How many can you find? It is considered that if you can find 10 faces you have normal powers of observation. If you find 15, you have above average observation skills, if you discover 21 or more, you have extremely keen observation skills. The faces that are most obvious are the ones in the foreground, along the path. They are lit up and our eyes are drawn naturally to them. The faces in shadow are perhaps more tricky to observe.
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