La Gioconda

All this will create the appearance of more life in the face. If the mind can unify two views, a further and higher dimension will sometimes be created. For example, if one takes an x-ray photograph of an object, then repeat this shot at a slightly different angle, after which the two x-ray negatives are placed on a stereographic viewer so that the images superimpose, the eye will not separate the two but unify them to create a vivid 3D view of the inside of the object.

Picasso was attempting something similar when he painted faces with two noses, or with double features. Inwardly he was sensing the greater dimensional perception of the unconscious and he wished to express more than the lifeless, frozen portrait of the third dimension. Unfortunately the conscious mind cannot even remotely accommodate these effects, and they do not succeed (they may have, however, from Picasso’s view, who would have an unconscious context of the greater whole, spanning space and time--giving his own prejudiced perception).

In the case of the Mona Lisa, the distortion, or ‘Picasso effect’--number (3)--by means of the complementary tricks described, can be interrelated as one whole--one does not see a distortion. But even so this will be an unconscious impulse coming through to the conscious mind intuitively. The conscious mind will tend to flicker from one state of observation to another but will experience unification of the shifts, creating the illusion of fluidity of form and greater expression. Thus the two displaced views of the face (compare the two x-rays) create depth and a more alive effect.

(source)

A nude version of the Mona Lisa is being shown in Milan. The naked portrait - titled the Monna Vanna, and complete with the model’s famous enigmatic smile - was painted in 1515 by Leonardo da Vinci’s pupil, Andrea Salai. Art historians say that it was not only inspired by Leonardo, but is almost certainly based on a lost original by the artist himself.
source: http://www.tomgrossmedia.com/art/archives/000334.html

Leonardo da Vinci painted two Mona Lisas - one clothed and one naked. The clothed one is now in the Louvre. This book will tell the story of how the nude version was painted, how it disappeared and where it is now. The one shown here is a copy painted in Leonardo’s studio by his pupil Giacomo Salai around 1515. It went on show for the first in Milan in November 2000.