List of Free WordPress CAPTCHA Plugins

reCaptcha 

★ Features- Protects from spam comments and form, Use on Login form, Registration form, Custom form, Testimonials, Contact Form, Reset password form.

(wordpress.org/plugins/google-captcha)

Really Simple CAPTCHA

★ Features- Executes temporary files, Easy to embed, Requires GD, Taking up very little space, allow the submitted form, including contact form and login form.

(wordpress.org/plugins/really-simple-captcha)

CAPTCHA 4WP

★ Features- Spam Protection, Set CAPTCHA passmark score,  auto detect language, Configure CAPTCHA properties, secure forms, option for hide captcha.

(wordpress.org/plugins/advanced-nocaptcha-recaptcha)

Login No Captcha reCAPTCHA

★ Features- Adds Google No Captcha checkbox, Ability to block automated scripts, WooCommerce login page, forget password page, and user registration page.

(wordpress.org/plugins/login-recaptcha)

Friendly Captcha

★ Features- Defend against bots, preventing spam, Protect users' privacy, Improve user experience, Scale reliably.

(wordpress.org/plugins/friendly-captcha)