Brave, which use it to filter it's Leo AI search, explain it very well. https://search.brave.com/help/pow-captcha Here, you can try a POW captcha, it's very straight forward, and you don't even notice your CPU is doing some computer calculations. Usually, when it comes to POW captchas, you can change the difficulty if you want to increase the filter. https://friendlycaptcha.com/