Ask HN: ReCAPTCHA Alternatives?

There is truth in this troll post: An individual and creative captcha solution won't be the target of mass attacks. If it requires to write a new program to solve it, and there is little gain (like only the ability to put spam on your blog post), chances are high a solution will hold.

A particular domain specific examples are math captchas such as https://math.stackexchange.com/questions/2266227/solving-mat... or https://packagist.org/packages/cismonx/math-captcha-polynomi... . While in general such captchas are seen as ridiculous, they ask for domain specific knowledge. A person who comments on a higher math related blog may find it easy to answer such a captcha.