Walk offers clues to identity

Because they have wider pelvises, women sway their hips more than men.

And people from one country can have a different gait to those in another.

What is of particular interest to scientists is trying to make a computer do what we all do instinctively - know within a split second that the lolloping or swaggering figure coming towards us is a close relative, a complete stranger, or one of our best friends.

Researchers at Georgia Tech in the US city of Atlanta are trying to teach computers to record the precise way we move.

Checking identities

Volunteers walk through a studio while wearing metallic disks. A computer monitors the position of each disk and builds up a digital picture of the person's gait.

When the computer analyses film shot in a different location, it identifies the volunteer as being the same person.

"Right now we're at the stage of verification," said Professor Aaron Bobick, associate professor of computational vision at Georgia Tech.

"If somebody comes in with an ID that says that's John, and then I see this person walking around outside can the computer tell that it really is John? The current performance levels are getting us close to being able to do that pretty well."

The security industry is interested in the technology as a way of picking a criminal out in a crowd.

The real challenge for scientists is to be able to recognise someone's gait out in the real world.

Lines of symmetry

At the University of Southampton in England, gait aficionados believe they are cracking that problem.

So we put them to the test. The first step was to generate a computer image of me walking through their lab.

Professor Mark Nixon of Southampton University explained: "We film as you walk and then we bung the film into computers.

"These then pull out a series of numbers, and each time you walk past the camera you should get the same set of numbers.

"A different person walks past and they produce a different set of numbers. We then recognise you by that set of numbers," he said.

Each person's walk is broken down into a computer image marking out lines of symmetry as the body moves.

Gait monitoring

The technique has only become possible in recent years as the power of microprocessors has accelerated.

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The question is whether the 7,000 gigabyte memory bank can tell me apart from everyone else it has stored.

In a bustling street the computer has difficulty separating me from all the other movement, but when I am the only person in shot there is no problem.

Another way to confuse the computer is to radically alter my walk. The lines of symmetry generated are so different to my normal walk that the computer is unable to recognise me.

If gait technology ever catches on as a security weapon could it be that criminals start looking for inventive ways to avoid being recognised?

Perhaps adopting someone else's walk will become the ideal way of foxing tomorrow's gait monitoring police.