It’s been getting harder to prove you’re a human online in recent years. The squiggly letters known as CAPTCHAs that protect websites against spam software have got more distorted, as the software has got better at reading them.
That was why I thought it worth noting when NuCaptcha launched its video CAPTCHAs, which are easier for humans but still secure and have been adopted by sites including Groupon. Now researchers at Stanford suggest they, too will have to become more cryptic.
Elie Bursztein led the research, and explains on his blog how he designed software that compared multiple frames from NuCaptcha’s videos to spot and decode the jiggling letters needed to enter a site protected by a NuCaptcha puzzle. Video CAPTCHAs require the use of techniques not used against the puzzles before to isolate the puzzle amongst everything else in the footage, says Bursztein. But once software has located the string, but also provide multiple copies of the same puzzle, which makes it easier to solve. He reports that software that identifies video frames showing the CAPTCHA then goes back to the video to track the movement of the letters to accurately isolate them for recognition can beat NuCaptcha with close to 100 percent accuracy.
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