Lip-reading computers that unlock with a word may soon become a possibility after a new study has found that every person moves their lips a little differently when they speak.

Ahmad Hassanat at the University of Mu'tah in Jordan trained software to look for patterns of lip and mouth movements associated with different words as people spoke to a camera - how much of the teeth were showing in any given video frame, for example.

From mouth movements alone, the system correctly identified the words being said nearly 80 per cent of the time, 'New Scientist' reported.

Hassanat also found that every person moved their lips a little differently when they spoke.

Even the best actor would find it impossible to exactly duplicate someone else's lip movements, Hassanat said.

This could mean that one day a "visual password" could work as a form of biometric security, even allowing people to log on to computers simply by having them watch their mouths as they speak