We can never know the world around us as it really is; we can only know it as our brains perceive it. The process of interpreting the signals that come to our eyes is quite complicated, but it works well for us most of the time. Optical illusions occur when our minds interpret visual signals incorrectly. When we began to record images outside our brains, we added a mechanical layer of interpretation that can also go slightly wrong. Then we started using several different methods of recording visual images, and the possibility of incorrect interpretation multiplied, leaving us with some weird camera effects, as you'll see in this article I posted at mental_floss.