Use in conjunction with the Captcha module to prevent spam on forms.
As of Jan 2020, still ONLY supports v2 of Google's reCAPTCHA API (there's an active issue for v3 support)
There's also an option for non-js fallback.
Tested with D7 and D8.
Patch needed for AJAX forms (e.g. Webforms with AJAX support turned on) to stop the ReCAPTCHA UI disappearing when page is reloaded.