Just a quick post pointing out an interesting bit of optical chicanery. Blogger Whale has an image that changes depending on how close you are.
The explanation given is to do with how the eyes focus close up and from a distance, and the resolutions at both of these points. Decoye Gheist has a plausible explanation. The image itself is made by superimposing the pictures after going through low pass filter and a high pass filter to create one half, and vice versa for the other.
Edit: Somehow the URL got edited out of the original post. I blame the byte fairies.