Before you start reading this, count the circles in the image below. How many are there (if there are any)? Also known as Coffer Illusion, this optical illusion was created by Anthony Norcia and qualified for top 10 category in “Best Visual Illusion Of The Year Contest”. Anthony describes this visual phenomenon like this:
First time viewers of this display invariably do not see the 16 circles segmented from the background. Rather, they see a series of rectangles that they frequently describe as “door panels”. The illusion pits segmentation cues against what appears to be a very strong prior to interpret the image as a series of 3-D structures “coffers” with closed boundaries. (A coffer is a decorative sunken panel.) It appears that the prior involves both closure and shape-from shading assumptions.