Check out this image. Up close we see Albert Einstein. But vision like other things can be relative. Now stand up, walk to other side of the room and take another look.
Strange huh? It turns out that our visual system is designed to pick up different levels of detail at different distances. Up close we pick up fine details. At a distance we pick up coarse details. This can allow us to see the image above as two completely different images. Read this article from the great neurophilosophy blog to get more information on this interesting phenomenon.