The hCaptcha extension adds a captcha to TYPO3 system extension form to stop spam/bots reliably. hCaptcha is a free-to-use service for sites of any size - you can even earn a bit of money with it. Find more information on their website:

It has a similar feature set to Google's reCaptcha, with a significant focus on privacy and GDPR-compliance.

hCaptcha rendered in frontend

Contact Form with hCaptcha protection.

The extension adds an advanced element Captcha to the TYPO3 form extension, which allows flexible usage of the captcha on a per-form basis.