Leaning Tower Illusion

The leaning tower illusion is a clever angle-perception illusion that won the 2007 award for the Best Iillusion of the Year. It was discovered by Ali Yoonessi, Elena Gheorghiu and Frederick Kingdom in Mcgill University.

The illusion consists of putting two identical images of a leaning tower (e.g. the tower of Pisa) side by side: the observer sees the second tower lean more, like if it was photographed from a different angle. The two images, however, are exacly the same.

The picture on the right appears to be angled: in reality, the two images are exacly the same, side by side, with no added angles.