Optical illusions or visual illusions are fascinating visual phenomena. Here is an amazing collection of cool illusions that will boggle your mind. Many of these illusion pictures can keep you engaged for hours. According to Wikipedia,"An optical illusion (also called a visual illusion) is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source. There are three main types: literal optical illusions that create images that are different from the objects that make them, physiological illusions that are the effects of excessive stimulation of a specific type (brightness, colour, size, position, tilt, movement), and cognitive illusions, the result of unconscious inferences". In this post we have added 20 mind blowing cool illusions to challenge your mind. If you enjoyed these cool illusions, please share them with your friends.