We see the popular "captcha" security mechanism often - wavy letters websites ask us to type into a box. It's used by web pages and newsletter sign-up forms to prevent computer robots from hacking into servers and databases. But these codes, which are becoming increasingly complicated for an average person to use, are not immune to security holes.

A research project led by Prof. Danny Cohen-Or of Tel Aviv University's Blavatnik School of Computer Sciences demonstrates how a new kind of video captcha code appears to be harder to outsmart. The foundation of the work, presented at a recent SIGGRAPH conference, is really pure research, says Prof. Cohen-Or, but it opens the door so security scientists can think a little differently.

"Humans have a very special skill that computer bots have still not been able to master," says Prof. 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".


A truly "emerging" technology

In the new research paper, co-authored with colleagues in Taiwan, Saudi Arabia and India, Prof. 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.........