Some brief excerpts from their paper:
We present a novel CAPTCHA which requires users to adjust randomly rotated images to their upright orientation ... Rotating images to their upright orientation is a difficult task for computers .... [Our] system ... results in a 84% human success rate and .009% bot success rate.The paper goes on to say that "no algorithm has yet been developed to successfully rotate the set of images used in our CAPTCHA system." The key word there is "yet." As soon as there is a strong incentive for people to develop better algorithms for this problem, better algorithms will be developed.
The main advantages of our CAPTCHA technique over traditional text recognition techniques are that it is language-independent, does not require text-entry (e.g. for mobile devices), and employs another domain for CAPTCHA generation beyond character obfuscation.
But, as Luis von Ahn insightfully pointed out in a recent interview in New Scientist, it is a perfectly fine outcome if spammers find a way to break this new image-based CAPTCHA technique. By doing so, they are helping us make computers smarter.
From the New Scientist article:
"If [the spammers] are really able to write a programme to read distorted text, great – they have solved an AI problem," says von Ahn. The criminal underworld has created a kind of X prize for OCR.
Security groups ... [then] can ... switch for an alternative CAPTCHA system -- based on images, for example -- presenting the eager spamming community with a new AI problem to crack ... Image orientation is difficult for computers. But if [image-based] CAPTCHA becomes common, it won't be long before spammers turn their attention to cracking the problem, with potential fringe benefits to cameras and image editing software.
Speech recognition CAPTCHAs are already being used, and image labelling ones could follow, says von Ahn. AI researchers are already working in both these areas, but they could soon be joined by spammers also helping advance the technology.
Perhaps it is time to start designing CAPTCHAs in a different way -- pick problems that need solving and make them into targets to be solved by resourceful criminals.