Kingdom FAA, Yoonessi A & Gheorghiu E (2007) The Leaning Tower illusion: a new illusion of perspective. Perception, 36 (3), pp. 475-477. https://doi.org/10.1068/p5722a
First paragraph: We would like to describe a new illusion of perspective that to our knowledge has not been reported before. Figure 1 shows two images of the Leaning Tower of Pisa placed next to one another. One obtains a strong impression that the tower on the right leans more, as if photographed from a different angle. Yet the two images are identical, as close inspection will reveal.
Perception: Volume 36, Issue 3