Perceptual Science Group @ MIT

Proof

The original image of the illusion

The squares marked A and B are the same shade of gray, yet they appear different.

The original image plus two stripes

By joining the squares marked A and B with two vertical stripes of the same shade of gray, it becomes apparent that both squares are the same.

I still don’t believe it. The must be something sneaky going on in those images. Show me more evidence.