Sounds like a good idea— so whats the catch?
1. Computers can break ’em anyway… although amateur programmers won’t have an easy time doing so. Greg Mori and Jitendra Mailk’s Breaking a Visual CAPTCHA discusses advanced techniques that can be used to crack even fairly sophisticated captcha systems. 2. Some humans can’t break ’em! Obviously, blind users can’t solve a visual captcha. Better captcha systems also offer an audio-based option. Even then, deafblind users (those who are both deaf and blind) are locked out. Sites employing captchas should at least consider offering special accounts to those with special needs in this area. One solution is to offer a telephone number— and make sure you accept TDD relay calls! These are voice calls placed through an interpreter. Your telephone support staff should be educated about this and encouraged to create accounts or carry out other captcha-protected tasks on behalf of legitimate users who contact you via phone. 3. Captchas can take up extensive CPU resources (that is, slow down your
