If CAPTCHA was only about trying to keep bots out of websites, it wouldn't be that hard. CAPTCHA is a profitable enterprise, because every user response is use

If CAPTCHA was only about trying to keep bots out of websites, it wouldn't be that hard. CAPTCHA is a profitable enterprise, because every user response is used to train an AI. It is presented as a free service for website owners, but actually it uses your users to be trainers. A truly free open-source captcha wouldn't be very hard to implement or to keep updated, but no one does it because it would be very expensive to host the server.