This illusion was created by specialists at Massachusetts Institute of Technology some years ago. It contains pictures of two famous people – Marilyn Monroe and Albert Einstein – superimposed on one another. Take a look at this gif.
Did you notice Marilyn Monroe turning into Albert Einstein as the image drew closer? No? You should visit an ophthalmologist. Take a look at this video by AsapSCIENCE to learn more about how this process tests your eyes.