Captchas does not stop scraping
CAPTCHA breaking outsourced
The Register has an article about recent troubles for Google with spammers registering free accounts. People in low cost counties is hired to manually break CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart), to create accounts later used to send spam using Googles resources.
CAPTCHAs broken in many ways
Not only humans is used to break CAPTCHAS. Earlier this year it was widely reported that Yahoo's CAPTCHA system was broken with software by security researchers from Russia. They released software able to decode images with a recognition rate of about 35%.
Microsoft also have the same problem with their free mail accounts. Websense reports on how Microsoft Windows Live Mail sign up procedure is broken by malware.
CAPTCHAs does not work to stop scraping. The advances in OCR-technology further accentuates the need for additional scraping mitigation solutions working together with captcha tests.