reCAPTCHA
reCAPTCHA is a free security service that protects your websites from spam and abuse.
4 Alternatives To reCAPTCHA
FeedCaptcha
FeedCaptcha is a new captcha system, easy to integrate and with meaning for your product.
MTcaptcha
Enterprise Captcha solutions
Securimage
Securimage is a script for generating complex images and CAPTCHA codes to protect forms from spam…
UniqPin
UniqPin is a free for non-commercial use service which destiny improve ability of interfaces detect…