Her enigmatic smile has teased art historians for centuries. But the eyes of the Mona Lisa also hold a secret.
Experts are trying to decipher tiny numbers and letters painted into the eyes of the portrait -- a mystery that could have come straight from the pages of 'The Da Vinci Code'.
Art historians found that by magnifying high-resolution images of Leonardo da Vinci's masterpiece symbols can be seen.
"To the naked eye the symbols are not visible, but with a magnifying glass they can clearly be seen," said Silvano Vincenti, president of Italy's National Committee for Cultural Heritage.
In the right eye appear to be the letters 'LV' which could stand for the artist's name, while there are also symbols in the left eye, but they are not as defined.
Mr Vincenti said: "It is very difficult to make them out clearly, but they appear to be the letters 'CE', or it could be the letter 'B'. You have to remember the picture is almost 500 years old so it is not as sharp and clear as when first painted."
He added: "While in the arch of the bridge in the background the number '72' can be seen, or it could be an 'L' and the number 'two'."
The painting -- which has long been steeped in mystery with the true identity of the sitter remaining far from certain -- featured in the Dan Brown novel 'The Da Vinci Code'.
The lead character interprets secret messages hidden in the Mona Lisa and da Vinci's other works, including The Last Supper.
Mr Vincenti said he was put on to the mystery after his fellow committee member, Luigi Borgia, found a musty book in an antique shop. The 50-year-old volume describes how the Mona Lisa's eyes are full of signs and symbols.
Mr Vincenti's committee is asking for permission to exhume da Vinci's remains from his tomb at Amboise Castle in the Loire Valley.
They want to see if the artist's skull is there so they can try to establish if the Mona Lisa is a self-portrait.
Some historians believe that da Vinci was homosexual and his love of riddles led him to paint himself as a woman. Other theories state that the sitter is Lisa Gherardini, the wife of a Florence merchant, or the artist's mother. (© The Daily Telegraph, London)