Does Big Ben look like it’s leaning over more in the right hand image than in the left hand one? It can take a double-take to spot that the two pictures are identical. I find it a fantastically strong illusion.
It’s a demo of a new illusion found by Frederick Kingdom and colleagues (you’ll need to scroll down that link to get to their bit – look out for an even more than usual Leaning Tower of Pisa). Their discovery is a new version of the size-constancy illusion. This is my second demonstration of it – a few posts back I used a picture of a historic streetlamp. But here’s an example that looks stronger to me, with a better known subject.
Update 10 Oct 2011. Big Ben really is leaning over! But not (yet) as much as it appears to lean in this illusion.