How to set up Google reCAPTCHA & invisible reCAPTCHA in Joomla
Google introduced a no CAPTCHA reCAPTCHA API in December 2014. The reCAPTCHA plugin, which protects your contact and registration forms against spam, has been updated in Joomla! 3.4.0. While still supporting the old reCAPTCHA 1.0, you can use the reCAPTCHA version 2.0. A significant number of your users can now attest they are human without having to solve a CAPTCHA. Instead with just a single click they’ll confirm they are not a robot!
As of Joomla 3.9, a new plugin CAPTCHA - Invisible reCAPTCHA has been added, allowing to use Invisible reCAPTCHA on your websites. It allows to validate requests in the background, your users don't have to perform any action to validate a form.