Behind the smile Mona Lisa

The true meaning behind Mona Lisa's mysterious smile has haunted art lovers for many years, but now scientists believe they have an answer.

With a computer program designed to identify facial emotions, they found that the beauty of Leonardo da Vinci had 83% happiness, 9% scorn, 6% fear and 2% anger.

The study was developed by Professor Nicu Sebe of the University of Amsterdam in the Netherlands, thanks to a face tracking software developed by teacher Tom Huang at the University of Illinois, USA.

By comparing the picture with key facial features, such as the curvature of the lips, the wrinkles on the corners of the eyes, the program can find indicators for the six basic human emotions: happiness, surprised, angry, scornful, scared and sad.

According to scientists, technology can be used to create computers that respond to users' moods.

There have been many theories about the identity of the beautiful woman and her smile. Some say that Mona Lisa was pregnant at the time, or actually it was a gay lover of a painter, or a self-portraying portrait.

Professor Donald Sassoon, of the University of London said: " One of the most important things about painting is that Leonardo used a technique called sfumato - meaning smog ."

When asked why Mona Lisa laughed, he replied, " How to know why people laugh in the picture. In the 15th century, everyone's teeth were so bad that they wouldn't want to show off ."