A computer has been used to decipher the enigmatic smile of Leonardo da Vinci's Mona Lisa, concluding that she was mainly happy.
The Mona Lisa became world famous after it was stolen in 1911
The painting was analysed by a University of Amsterdam computer using "emotion recognition" software.
It concluded that the subject was 83% happy, 9% disgusted, 6% fearful and 2% angry, New Scientist magazine was told.
The computer rated features such as the curvature of the lips and crinkles around the eyes.
The program, developed with researchers at the University of Illinois, US, draws on a database of young female faces to derive an average "neutral" expression.
The software uses this average expression as the standard for comparisons.
The New Scientist says that software capable of recognising emotions just by looking at photographs could lead to PCs that adjust their response depending on the user's mood.
Possibly the most famous portrait of all time, Mona Lisa's cryptic expression has intrigued art lovers for five centuries.
In 2003, a scientist from Harvard University said the way the human eye processes visual information meant the smile was only apparent when the viewer looked at other parts of the painting.
The painting, which is on public display in the Louvre in Paris, was painted between 1503-1506.
It was thought to be named after the sitter, most likely the Florentine wife of Francesco del Giocondo.
The Mona Lisa features in the opening of Dan Brown's hit novel The da Vinci Code when a Louvre curator is found dead near the painting.