I was looking around Google and I found a site with a large number of optical illusions on it. I think one of the best ones on the site (even though it states it isn't a proper optical illusion) is this picture of a skull. Except that it really isn't a picture of a skull unless you blur it. The original painting is of something entirely different. It is possible that the artist painted the picture with the two different pictures in mind but you'll have to decide that for yourself. Once you click over to the site, mouse over the image to find out what it really is. Additionally there is a second skull painting here (though not as well done).

Find out what the skull really is.