Researchers at the University of Stirling found people who lied could not hide their reaction when shown a photo of a familiar face.

They used a process which tracks an individual's eye movements while they looked at images on a computer screen.

A similar process is used by police in Japan to uncover guilty knowledge about crimes.

The ConFace project was led by Dr Ailsa Millen, research fellow in psychology at Stirling University, who explained people often lie to police to protect criminals' identities.

"Police officers routinely use photographs of faces to establish key identities in crimes," she said.

"Some witnesses are honest - but many are hostile and intentionally conceal knowledge of known identities.

"For example, criminal networks - such as terrorist groups - might deny knowledge to protect one another, or a victim might be too afraid to identify their attacker."

'Markers of recognition'

The researchers used a process known as the concealed information test (CIT), where eye movements are tracked.

In each test, participants denied knowledge of one familiar identity and correctly rejected unfamiliar faces by pressing a button and saying 'no'.

It was found that most people could not hide their reaction if they recognised a face.

And the more people tried to cover up their knowledge, they produced more "markers of recognition".

Dr Millen said: "Instead of looking for signs of lying directly, we looked for markers of recognition in patterns of eye fixations - such as how individuals looked at a photograph of someone they recognised, compared to someone they did not.

"The harder that individuals tried to conceal knowledge, the more markers of recognition there were. These results suggest that it is difficult to conceal multiple markers of recognition at the same time."

"The main aim was to determine if liars could conceal recognition by following instructions to look at every familiar and unfamiliar face with the same sequence of eye fixations - in short, they could not."

While the CIT is used in Japan, little research has examined the process being used with faces.

The Stirling team consulted with colleagues in Japan, including Professor Shinji Hira, a CIT expert at Fukuyama University.

The ConFace project is funded by the University of Stirling and the Economic and Social Research Council (ESRC).