The Leaning Tower Illusion was reported by Frederick Kingdom, Ali Yoonessi, and Elena Gheorghiu of McGill University. In it, two identical side-by-side images of the same tilted and receding object appear to be leaning at two different angles. This effect was first reported in 2007 in images of the famed Leaning Tower of Pisa, but it also works with paired images of other tilted objects. Their findings won the 2007 Best Visual illusion of the Year Contest
The twin Petronas Towers in Kuala Lumpur seen in the same picture do not have the same effect because they appear to converge at at distant point. this does not happen in side by side images like as seen in the Leaning Tower effect
The Leaning Tower Illusion also works with paired images of train tracks, violating the rules of perspective.
However, the illusion does not occur when viewing two leaning Japanese manga girls, even though the two cartoon images are tilted because the images do not recede in depth.
More references http://www.scholarpedia.org/article/Leaning_tower_illusion