We often see websites asking us to key in wavy letters into a box to prevent computer robots from hacking into servers and databases. But these codes, which are becoming increasingly complex for an average person, are not immune to security breaches.

A project led by Danny Cohen-Or, computer science professor at the Tel Aviv University (TAU), shows how a new kind of video captcha code may be harder to outsmart. Captcha technology is intended to block spam e-mail and automated systems.

“Humans have a very special skill that computer bots have not yet been able to master,” says Cohen-Or. “We can see what's called an 'emergence image' – an object on a computer screen that becomes recognisable only when it's moving – and identify this image in a matter of seconds.”

“While a person can't 'see' the image as a stationary object on a mottled background, it becomes part of our gestalt as it moves, allowing us to recognize and process it.”

The study was co-authored with colleagues in Taiwan, Saudi Arabia and India. Cohen-Or describes a synthesis technique that generates pictures of 3-D objects, like a running man or a flying airplane.

This technique, he says, will allow security developers to generate an infinite number of moving “emergence” images that will be virtually impossible for any computer algorithm to decode.

'Emergence,' as defined by researchers, is a unique human ability to collect fragments of seemingly useless information, then synthesize and perceive it as an identifiable whole.

So far, computers don't have this skill. “Computer vision algorithms are completely incapable of effectively processing emergence images,” says Cohen-Or's colleague and study co-author Lior Wolf.

The scientists warn that it will take some time before this research can be applied in the real world.”We're not claiming in our research paper that we've developed a whole new captcha technology,” says Cohen-Or.

“But we are taking a step towards that – something that could lead to a much better captcha, to highlight the big difference between men and bots,” concludes Cohen-Or.

“If it were to be turned into a solution, however, we wouldn't be able to give humans a multiple choice answer or common word answer for what they see, so we'll need to develop a way to use it. We have a few ideas in the works.”

The researchers are also developing methods of automatically generating “hidden” images in a natural background, like a pastoral mountain setting – a digital “Where's Waldo?” game.

“We're trying to hide images like eagles or a lion in mountainscape,” says Cohen-Or. Because the moving image blends into a static background, it's hard for bots to understand what the human eye perceives with only minimal training.