The discovery of a second version of Leonardo da Vinci's Mona Lisa, painted from a slightly different visual viewpoint from the original artwork, suggests the Italian master created his famous portrait as a 3-D image.

That, at least, is the latest theory about the 16th-century masterpiece, promoted by two psychologists from Germany.

The original Mona Lisa currently hangs in the Louvre in Paris while its slightly-skewed second version is displayed at the Prado Museum in Madrid, Spain.

Psychologists Claus-Christian Carbon and Vera Hesslinger, from the University of Bamberg, say in a study published last year in the journal Perception, and also in a future article in the journal Leonardo, that the slight variation in perspective between the two images creates a 3-D effect when they're combined.

(You can test their assertion for yourself, either by breaking out your personal pair of 3-D glasses or, if you are one of the people who can, stare at the two images slightly cross-eyed to see the 3-D effect.)

Although the researchers note it's not yet clear what da Vinci actually intended, "the Prado version and the Louvre version, generated in Leonardo's studio about 330 years before Wheatstone invented the stereoscope, can be combined to an image of Mona Lisa that has obvious stereoscopic qualities," the study said.

By looking at the differences in perspective between the two paintings, such as the positioning of Mona Lisa's nose, the two researchers have speculated on the setup da Vinci and the copy's painter (likely one of his students) might have used.

The painting presumably created by the student provides a 69-millimeter difference in perspective from the long-known work, approximately the distance between the typical Italian man's eyes, or an interocular distance of 64 millimeters, the researchers said.

As it turns out, establishing that type of visual offset is exactly how 3-D images are created.

Human brains perceive depth by combining the images from each eye, which, of course, capture a scene from a slightly different perspective.

Again, the researchers have yet to find evidence that da Vinci was, indeed, focused on introducing the world to a whole new way of perceiving visual art. The only thing they do know for sure is that the ability to appreciate one of the greatest paintings on Earth -- has been taken to a whole new dimension.