Google reCAPTCHA app is an easy-to-use app that protects your community from spam registrations and malicious bots. This integration would verify the authenticity of a web visitor, i.e., it'd find whether the visitor is a human or a bot.
Once this app is configured correctly, a CAPTCHA challenge would appear on the community registration page and new members would be allowed to sign up after solving the challenge. You can configure the type of challenge and complexity scale directly from Google's Admin Console.
Allow your users to log in to the community with their existing credentials
Allow users to quickly sign up with social media accounts they already use
Allow users to access the full content only after signing up
Improve the deliverability of the transactional emails from the community