To get around captchas spammers hire companies employing human solvers in Bangladesh, China and India at about $0.80 to $1.20 for each 1,000 solved captchas. Another approach involves copying the captcha images and using them on another site, often one offering free pornography in exchange for filling out a captcha.
With enough traffic, the attacker can get the solutions in time to relay it back to the target site. These methods have been used by spammers to set up thousands of accounts on free email services such as Gmail and Yahoo!. Since Gmail and Yahoo! are unlikely to be blacklisted by anti-spam systems, spam sent through these compromised accounts is less likely to be blocked.
The Daily Omnivore 
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