Illusions, the fun and interesting tricks for the eye, are caused by the specific ways the eye interprets images. All the images that the eye sees have important constraints on them, as discussed in the previous sections. There are many kinds of illusions and many different causes.
One major cause of illusions is that light entering the eye is captured on the 2-dimensional surface of the retina. Because the human eye always transforms these 2-dimensional images into a three-dimensional view, it is possible to make other two dimensional images appear three-dimensional. Other illusions occur if there is more than one way of interpreting an image. A person's visual system can only interpret images in one certain way at any given time. If an image is created on the retina, the brain may flip back and forth between interpretations of what that image represents. These are just two of the many visual "tricks" that can be used by taking advantage of the constraints of human sight.
This section is a gallery of visual illusions. The images on these pages will show you how easy it is for the eye and brain to misinterpret visual stimulations and create fun and interesting illusions.