LONDON - Criminals are going to have a really tough time hiding their faces, thanks to a new software that can recreate their faces.

The software is being used by approximately 15 police departments in the UK as well as half a dozen European countries, including France and Switzerland.

In field trials conducted by the Derbyshire police force, it led to twice as many identifications of suspects as traditional methods.

Law enforcement agencies worldwide traditionally employ sketch artists, who piece together faces.

The witness describes key features — such as hair length, nose size or sharpness of the chin — and the artist combines them to create a likeness. Some departments now have computer programmes that follow the same approach as these artists, creating facial composites using databases of pre-drawn features.

The problem with this approach, says Christopher Solomon of the University of Kent, who developed the software, is that it doesn't take into account how memory actually works.

"There's quite a bit of research in the psychology field suggesting that we're not so good at this, at recalling and describing a face," says Solomon.

His software known as EFIT-V system, generates its own faces that progressively evolve to match the witness's memories. The witness starts with a general description such as "I remember a young white male with dark hair."

Nine different computer-generated faces that roughly fit the description are generated, and the witness identifies the best and worst matches. The software uses the best fit as a template to automatically generate nine new faces with slightly tweaked features, based on what it learned from the rejected faces.

The mathematics underlying the software is borrowed from Solomon's experience using optics to image turbulence in the atmosphere in the 1990s.

"I then realized that the same technique could be applied to human faces, which in many respects are mathematically similar to turbulent wave fronts," says Solomon.

One advantage of this technique, says Solomon, is that it can be used on witnesses who can't recall details about a suspect — but say that they would remember the face if they saw it again.