Using computers to recognise faces in old paintings is more challenging than picking out faces in a crowd. Facial recognition struggles with changes in pose, illumination, facial expressions and ageing. But in works of art, the computer must contend with the quirks of the artists’ styles. Another major hurdle is that often, precious few contemporary paintings exist on which to train the computer.
To improve its chances of finding a match, the program works out the best combination of facial measurements and discriminating features with which to look for matches.
(source: accessed 16 Feb 2015)