Modern CAPTCHAs often don’t require you to click anything, or will let you just check a box. I gather they are monitoring stuff like keyboard and mouse events on the page and can identify bots based on the timing of scrolls and clicks and what not. Those patterns are specific to the page, and hard to fake without empirical data from real users, which the page owner has but bots don’t.
When they do ask you questions, it may be mostly or entirely for their own selfish purposes. They show you some pictures they’re confident about (positive or negative), mixed in with some where they’re less confident. If you disagree with them on a confident match then you’re a witch. If not, they will take your opinion on the non-confident matches, and combine it with a bunch of other people’s opinions to get some useful training data. Potentially, since they’re tracking the shit out of you, they can eventually weight your answers based on how good you are at identifying things.
Basically, they’re not asking you “what is this image?”, they’re asking you to vote on whether the decision they’ve already made is correct.
