... According to a recent study, about 25% of users' attempts to solve CAPTCHAs from reCAPTCHA simply fail. For businesses that use services like reCAPTCHA, this means that a quite a few of potential users are likely to abandon the registration or shopping process.

NuCaptcha argues that 99% of its users are able to solve the company's video CAPTCHAs. While we can't test the company's numbers, we did get a chance to test the system, and the tests were indeed very easy to solve.

As the company's CEO and co-founder Michel Giasson told us earlier this week, it is extremely easy for humans to solve these moving CAPTCHAs. Machines, however, have a very hard time with this. To discourage paid human "solvers," the company uses sophisticated machine learning algorithms to detect potential abuse of the system and then slows the video CAPTCHA down to the point where solving it becomes too time consuming and costly. According to Giasson, professional human CAPTCHA solvers need about four seconds per CAPTCHA. When NuCaptcha suspects that sombody is abusing the system, it can slow its text scroll down to the point where it takes more than 15 seconds to even display the CAPTCHA text.

Read More:
http://www.nytimes.com/external/readwriteweb/2010/06/30/30readwriteweb-video-captchas-promise-better-security-less-17052.html