This qr code gave me a 99% discount on all walmart items!
It shows a donut and it says "eat it!"
It's called a stereogram.
Oh, and the picture has to be quite big to fool your brain.
Its easier if you cross your eyes, try to "unfocus" then decross your eyes. After some tries, you should see the doughnut. Because of the eye-crossing, its inverted. Its easier to do than the normal way (for me). Also, your eyes may just get stuck in that position. Use at your own risk! xD