Optical illusions has always been a curiously fun and dizzying experience for me.

One that has particularly caught my eye is the "moving image" optical illusion, also known as illusory motion, where an static image appears to be moving due to cognitive effects. A lot of these images work based on your peripheral vision, resulting in something called the periphery drift illusion (PDI).

Note that when you stare at one spot, that one spot stays static, but everything around it (everything in your peripheral vision) appears to be moving. This is due to rapid eye movements or blinks and changes in lighting that trick the periphery into perceiving motion when there isn't any. Since motion is perceived in a dark-to-light direction, the images will move accordingly.

In other words, the image will appear to be moving if you don't look directly at it. This also explains why this illusion doesn't work as well on small images because then there is not much in your periphery (so full screen these images and look to the side for the full effect!

The periphery drift illusion was first documented by Jocelyn Faubert and Andrew Herbert in 1999 in Perception, a scholarly journal. Since then, acclaimed Akiyoshi Kitaoka, a Professor of Psychology, renowned for his optical illusions, has accumulated a great amount of designs over the years and really popularized this illusion. One famous example would be: