reCAPTCHA is a free service powered by Google that protects your website or funnel from spam and abuse. reCAPTCHA uses an advanced risk analysis engine to keep automated software from engaging in abusive activities on your site.
reCAPTCHA v2 is represented by the "I'm not a robot" checkbox you might see on different websites. It will either pass the user immediately or challenge them to validate whether or not they are human.
With the help of CF Power Scripts, you can easily add reCAPTCHA v2 to your funnel pages to prevent bots from opting-in.