UsersWP ReCaptcha
The UsersWP Re-Captcha plugin allows you to implement a Google security captcha into forms like registration and login forms. UsersWP Re-Captcha protects your site against spam, malicious registrations and other forms of attacks where computers try to disguise themselves as a human.
UsersWP Re-Captcha provides some of the smartest anti-spam security by protecting your site against spam and malicious registrations..