This is painting of St. George and the Dragons in by Sandro del Prete and a wonderful example of art and subliminal messages. When you look closely at the face, you can easily see a dragon fighting against a knight. I found this on Subliminal Messages of the World.
According to the author, if you are able to see only one image more than the other, it means that conscious mind is dominating your subconscious mind, yet, your subconscious mind still registers the image that the conscious mind doesn't see.
Pretty cool stuff!