Mona Lisas side-by-side from the Louvre and Prado Museums - Getty Images
Like a classic ViewMaster toy, Leonardo da Vinci may have created his Mona Lisa in 3D.
German researchers studying the original in the Louvre and a copy in Spain say the two images are from a slightly different perspective - so that da Vinci was playing with 3D. As evidence, they say that two Monas were observed from a point 2.7 inches apart - about the distance between your eyes.
They say the two images can be combined as a stereoscopic image with real depth. In other words, Leonardo made the first 3D image.