I saw this on a blog entry recently on FireWire and was intrigued my the idea. I still find it fascinating.
It works using a hidden camera and then moving motorised wooden tiles (sort of wooden "pixels") to reflect the light. What a really cool idea. The Utube video included on the blog above shows some close-ups towards the end of the clip where it becomes clear how it works.
What a really neat idea! A wooden mirror. Who'd have thought of that!