elrata_

NOTE: I’m looking for a new maintainer. Please reach out to 
rodrigo@sdfg.com.ar if you are interested.
NOTE: I don’t have wordpress 5 installations to try this and plan to stop 
updating it. If this is a big issue for you, please let me know so I can 
consider to continue doing it. Also, let me know if you are willing to help with testing :).
This is a small modification of the wp-recaptcha plugin to make it work with 
BuddyPress. Currently uses recaptcha v2.
You only need this plugin if you use Buddypress with wordpress and want a 
recaptcha at the registration page.
It is always rebased on top of wp-recaptcha. See 
https://github.com/rata/wp-recaptcha-bp for more info
What is reCAPTCHA?
reCAPTCHA is a free CAPTCHA service that protects your site against spam, malicious registrations and other forms of attacks where computers try to disguise themselves as a human; a CAPTCHA is a Completely Automated Public Turing test to tell Computers and Human Apart. reCAPTCHA comes in the form of a widget that you can easily add to your blog, forum, registration form, etc.
In addition to protecting your site, reCAPTCHA also helps us digitize old books and newspapers, transcribe street numbers and solve hard AI problems. <a href="http://www.google.com/recaptcha" rel="nofollow ugc">Learn how reCAPTCHA works</a> and join our <a href="https://groups.google.com/forum/#!forum/recaptcha" rel="nofollow ugc">forum</a>.
<h3>Requirements</h3>
<ul>
<li>You need the reCAPTCHA keys <a href="https://www.google.com/recaptcha/admin#whyrecaptcha" rel="nofollow ugc">here</a>.</li>
<li>Your theme must have a <code>do_action('comment_form', $post->ID);</code> call right before the end of your form (Right before the closing form tag). Most themes do.</li>
</ul>

WP-reCAPTCHA-bp

Integrates reCAPTCHA anti-spam methods with WordPress sites using BuddyPress plugin, including comment and registration spam protection.

WP-reCAPTCHA-bp vs hCaptcha for WP