This painting is titled The Ambassadors. It was painted by Hans Holbein the Younger in 1533 and depicts the aristocrats Jean de Dinteville and Georges de Selve. Jean de Dinteville (on the left) was the French ambassador to England whose motto was Memento mori, or "Remember, you will die." His friend Georges de Selve had just been appointed Bishop of Lavaur when the painting was commissioned. The painting now hangs in the National Gallery in London. While there are quite a few interesting objects in the picture, all of which have meaning, what's that on the floor? At first glance, it looks like a sword. Or maybe a piece of wood. It's actually an optical illusion of a type called anamorphosis. This video will make it clear.
Read more about the illusion at Creative Bloq. If you're interested, you can explore the symbolism of the other objects in the painting at Wikipedia. -via Damn Interesting