There are 16 circles hidden in the picture. The first is highlighted above, and the rest should now be easy to perceive.
This fascinating image was created by Anthony Norcia of The Infant Vision Laboratory at Smith-Kettlewell. It is referred to as the Coffer Illusion due to its close resemblance to the 3-dimensional coffers usually found on wooden doors (a coffer is a decorative sunken panel). Dr. Norcia claims that the illusion works because segmentation cues are pitted against the observer’s strong conviction to interpret the image as a series of rectangular coffers with closed boundaries.
When Dr. Norcia tested this illusion on a group of 100 people, the average time taken to see the circles was 45 seconds. A few individuals were able to spot the hidden shapes after only 10-15 seconds, while other persons took much longer and/or required explicit hints to finally see the circles. How long did you take?