Can you see a head here? Bots hopefully can't.
Moving blots to defeat Internet bots
Published 03 November, 2009, 17:39
Edited 07 November, 2009, 13:02
The next-gen version of captcha, a variety of tests used on Internet website to tell real living humans from spamming bots, may be using animated pictures resembling paper sprayed with ink.
Today to register at a new website you usually have to type a combination of distorted and masked characters from a displayed picture. This is supposed to verify that you are not a program trying to unload a bunch of spam on other users. The problem is that text-recognition programs are becoming more sophisticated and bots are learning to pass these tests.
A team of computer scientists from India, Israel and Taiwan have created what they believe will be an airtight fence in the way of future bots. Their system is based on the way the human brain can pick up seemingly unrelated elements and construct a whole image from them, reports New Scientist.
Software developed by the researchers takes a 3-D model of an object and identifies key features that a human mind will be able to anchor to recreate it. Then the image is transformed into an array of ink blots and placed on a background of random blots that camouflage it.
During tests of the algorithm conducted by the team, 310 volunteers were shown blotted images with various levels of background noise and number of object splats. On “easy” setting, 98% of the emerging images could be recognized by at least 80% of the subjects.
However, the success rate dropped to just 74% as the researchers moved to “hard” mode, similar to what happens to common captcha systems as they become better disguised to beat the bots. It also took users twice as much time the average, or over 12 seconds, to identify the objects.
This problem can be solved by using an animated sequence instead of a still image. On a video, a moving shape is easily distinguishable, while in individual frames the recognition rates were as low as 9.6%.
"When we add motion we win on two fronts," says Niloy Mitra at the Indian Institute of Technology in Delhi, who was involved in the project. "Recognition becomes much easier for humans and much harder for bots."
The team is to present their work at the SIGGRAPH Asia conference in Yokohama, Japan, in December.
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