Amazing Checker Shadow Illusion

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.

The images we see are not always true to reality. Our brains are pretty cool. If you are still not convinced, use the color dropper in your photo-editing software. Mind = Blown.