Optical Illusions

Seeing feels effortless, but your brain is working hard: guessing sizes, distances, colors and movement from the light that reaches your eyes. Usually it guesses right. These 176 illusions catch it guessing wrong. Open one, make your guess, then see the answer and why.

Bigger or smaller?

Your eyes don’t measure sizes the way a ruler does. Your brain compares each thing with what’s around it, and guesses how far away it is.

Straight, bent or tilted?

Every line in these pictures is perfectly straight, parallel, or round. The patterns around them make your brain bend them.

Lighter or darker?

You don’t see how much light comes from a spot. You see it compared with what’s around it, and you see what your brain thinks the thing really looks like.

Tricks of color

Color isn’t only in the light. Your brain decides what color things are from their surroundings and the light it thinks is shining on them.

Tired eyes

Stare at one thing for a while and the cells in your eyes and brain get used to it. Then they show you the opposite, or stop seeing it at all.

Shapes that aren’t there

Your brain is built to find objects, so it sees edges and shapes where there are only hints of them.

Still pictures that move

Nothing on this page is moving, but your eyes say otherwise. Look around the pictures instead of staring at one spot.

Tricks of motion

Your brain builds smooth movement from a series of glimpses, which is why films and cartoons work, and why it can be fooled.

Toys that make pictures move

Before films, toys used the same tricks of the eye to bring drawings to life. You can make them all at home.

Two pictures in one

These pictures can be seen in two ways, but never both at once. Watch your brain flip from one to the other.

Impossible objects

Each part of these drawings makes sense, but together they make a thing that couldn’t be built.

Faces everywhere

We are so good at faces that our brains see them everywhere, and get confused when one is upside down or inside out.

Fooled by depth

Your eyes see a flat picture, and your brain turns it into a 3D world. Artists and scientists have found many ways to trick that step.

Out in the world

Some illusions happen outdoors: in the sky, on the road, and on the mountains.

Puzzles that fool the eye

Not quite illusions, these puzzles make you see, or say, something that isn’t true. Can you find the trick before you read it?

The pictures come from Wikimedia Commons, under the licenses shown with each one. Some famous illusions, like the photo of The Dress, aren’t here because their pictures can’t be shared freely.