Recaptcha

Tough on bots. Easy on humans.

reCAPTCHA is a free service that protects your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive CAPTCHAs to keep automated software from engaging in abusive activities on your site. It does this while letting your valid users pass through with ease.

Using advanced risk analysis techniques, it considers the user’s entire engagement with the CAPTCHA and evaluates a broad range of cues that distinguish humans from bots.