Computer scientists from the University of Amsterdam's (UvA) Faculty of Science recorded the smiles of visitors to the NEMO science centre in Amsterdam. The smiles of these 481 participants, of a wide range of ages, from all over the world, now form the most comprehensive smile database ever collected.

Theo Gevers and his colleagues Albert Ali Salah and Hamdi Dibeklioglu studied precisely what happens to your face when you smile, in hopes of using computers to automatically estimate the age of a person, to recognise emotions, and to analyse human behaviour.

From each subject, a posed smile and a genuine smile were captured on video. They also had to pose as angry, happy, sad, surprised, and scared. Certain characteristics, such as the speed with which the corners of the mouth move upwards, were analysed. The researchers also asked the subjects to look at images of other subjects and estimate their ages and rate their attractiveness.

The researchers used the collected data to develop software that can estimate the age of a subject. This software takes into account whether someone is happy, sad or angry, and adjusts the age estimates accordingly.

The software also appears to be slightly better in estimating ages than people: humans estimate ages with an error margin of seven years, whereas the computer has a margin of six years.

Together with colour scientist Dr. Marcel Lucassen, the group also found that females look younger when they smile, but only if they are over 40. If they are under 40, they should look neutral if they want to seem younger.

The research was conducted as part of the project Science Live, sponsored by the Netherlands Organisation for Scientific Research (NWO) and the Royal Netherlands Academy of Arts and Sciences (KNAW). You can see samples here.