Most effective form of CAPTCHA?

Question

Of all the forms of CAPTCHA available, which one is the \"least crackable\" while remaining fairly human readable?

Answer 1

Death by Captcha can solve any Regular CAPTCHA (incude reCAPTCHA), but not Speedcoin Cryptocurrency Captcha.

Death by Captcha - http://deathbycaptcha.com

Speedcoin Captcha - http://speedcoin.co/info/captcha/Speedcoin_Captcha.html