From PBS - It is the most famous painting in the world, created by the hand of a genius, marvelled at by millions every year in the Louvre in Paris--but could there be a second Mona Lisa? In 1913, an interesting portrait surfaced, the so-called "Isleworth Mona Lisa." Using sophisticated scientific analysis, scientists will test both paintings to determine whether Leonardo da Vinci painted an earlier version of the iconic portrait.