New captcha technique could foil robot hackers

Posted by Emma Woollacott

Scientists at Tel Aviv University are working on a new captcha technology which they reckon will be harder for robot hackers to bypass.

The new system relies on people's ability to recognise objects when they move, even though they may be much harder to see when stationary.

"Humans have a very special skill that computer bots have not yet been able to master," says Professor Danny Cohen-Or. "We can see what's called an 'emergence image' — an object on a computer screen that becomes recognizable 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 new synthesis technique generates pictures of 3-D objects like a running man or a flying airplane. This, says Cohen-Or, will allow security developers to generate an infinite number of moving 'emergence' images that will be virtually impossible for any computer algorithm to decode.

The scientists warn that it will take some time before the research can be applied in the real world. But they are currently defining parameters that identify the perception difficulty level of various images that might be used in future security technologies.

"We're not claiming in our research paper that we've developed a whole new captcha technology," says Professor 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.
"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."