reCAPTCHA

reCAPTCHA is Google's bot detection, now sold as reCAPTCHA Enterprise on Google Cloud. The current versions score each interaction in the background (0 to 1) based on behavior and Google's view of the browser, and you decide what to do with low scores: block, add friction, or send to review. Enterprise adds account defender (detecting takeover and credential stuffing), password leak checks and fraud prevention for payments.

The older checkbox and image challenge versions still exist for legacy sites. Everything requires a Google Cloud project, and the free allowance was cut in 2024, so plan for a bill above hobby volume.