[jwilkins]

CAPTCHA comes from "Completely Automated Public Turing test to tell Computers and Humans Apart". These tests don't fulfill that requirement.

Random guessing gives you 3%, which is worse than random guessing on either the MSFT or reCAPTCHA.

This is far worse though. A simple loop over the 30 positions, running the output through an OCR engine would give you nearly 100%.

FWIW, I wrote the paper and AFAIK was the first person to break reCAPTCHA. I worked on the original MSFT Passport/Hotmail CAPTCHA system and improved MySpace's CAPTCHA which took spammer registrations from ~1,000,000/day (automated) to a few thousand (manual) in late 2007.