Image caption Our faces betray a range of emotions; the thermal sensor even detects changes in blood vessels

A sophisticated new camera system can detect lies just by watching our faces as we talk, experts say.

The computerised system uses a simple video camera, a high-resolution thermal imaging sensor and a suite of algorithms.

Researchers say the system could be a powerful aid to security services.

It successfully discriminates between truth and lies in about two-thirds of cases, said lead researcher Professor Hassan Ugail from Bradford University.

The system, developed by a team from the universities of Bradford and Aberystwyth in conjunction with the UK Border Agency, was unveiled today at the British Science Festival in Bradford.

This new approach builds on years of research into how we all unconsciously, involuntarily reveal our emotions in subtle changes of expression and the flow of blood to our skin.

We give our emotions away in our eye movements, dilated pupils, biting or pressing together our lips, wrinkling our noses, breathing heavily, swallowing, blinking and facial asymmetry. And these are just the visible signs seen by the camera.

Even swelling blood vessels around our eyes betray us, and the thermal sensor spots them too.

Real-world test

Traditional lie detection depends on the venerable polygraph, first developed in 1921, a much more invasive apparatus with a set of wires attached to the skin. This new device promises non-invasive, even covert truth tests in real time.

"We bring together all this well-established work on expressions, these recent developments in thermal imaging, techniques for image tracking of subjects and our new algorithms into one operational system," said Professor Ugail.

Media playback is unsupported on your device Media caption A computer programme is used to monitor tiny changes in facial expressions

So far, the team has only tested its lie detector on willing volunteers rather than in a real-life, high stakes situation. Later this year, though, they plan to deploy it in a UK airport, probably running alongside experienced immigration officers as they conduct security interviews. The algorithms can then be tested against the verdicts of these officers.

"In a real, high-stress situation, we might get an even higher success rate," noted Professor Ugail, who believes he'll eventually be able to detect around 90% of those who are lying, which is similar to the performance of the polygraph.

The researchers acknowledge, though, that these tests can never be 100% accurate.

What they detect are emotions, such as distress, fear or distrust, and not the act of lying itself. Fear can sometimes be the fear of not being believed rather than the fear of being caught.