Of course, given some bots relay the captchas to humans, this arguably works best for a site with a specific niche in mind, since they can ask a significantly more difficult question that only someone interested in the topic would know.
Like say, how a PhD maths related community or blog might ask a university level maths question, a chess forum may ask a chess related one and one about a certain gaming franchise might ask questions about said franchise. Bonus points for keeping out people with no genuine interest in the topic.
Of course, given some bots relay the captchas to humans, this arguably works best for a site with a specific niche in mind, since they can ask a significantly more difficult question that only someone interested in the topic would know.
Like say, how a PhD maths related community or blog might ask a university level maths question, a chess forum may ask a chess related one and one about a certain gaming franchise might ask questions about said franchise. Bonus points for keeping out people with no genuine interest in the topic.