How many circles can you spot? Hint: There’s 16 circles and 9 lesser complete circles. Focus on the X to see them.

The leaning tower illusion won the Best Visual Illusion of the Year Contest 2007 first prize. A simple illusion but strikingly novel. The two photos of the leaning tower of pisa are the same but one has the impression that the right side leans more.

Source: Neural Correlate