Let’s exercise our eyes and also our mind by looking at few optical illusions.
The image below is a beautiful portrait of Mona Lisa hidden behind the lines. In fact these lines create an interesting effect.
The next one is a classic one. It’s one of those illusions which looks like its moving, but matter-of-factly its completely still. This wonderful illusion was created by A.Kitaoka in 2004.
The next one forms an interesting afterimage. 
Here’s a fast fact. The image gives an afterimage effect, which is also shown by the Amazing Dots. An afterimage is a visual impression that remains in the retina after the initial stimulus is removed; however the afterimage is the opposite colour to the original. So if you stare at a black square for a long time and then look away, the after image will be a white square. This image is effectively a ‘negative’ image of a face; after you have looked at it for a while, the afterimage is the normal face.
The next one is a clear example of pictographic ambiguity, where a single drawing has more than one ‘image’ within it, depending on how you look at it. 
This picture, My wife and my mother-in-law, is a particularly good example, and was published in 1915 by the cartoonist W E Hill. Even experienced psychologists can sometimes find this hard. Here’s a clue – the chin of the young woman becomes the nose of the old lady.
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