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It's just a concept, not a real test.

Captcha are already expensive at scale due to escalating checks when abuse is detected. You have to orchestrate and pay for residential proxies, containers with different fingerprints, different behavioural data, clean IP rep, emulate device performance to avoid revealing youre running on a server... A 1-shot doesn't scale against this.

If the payoff is worth it, no captcha is too expensive.

OP said "already expensive"; you said "too expensive". Both can be true.

unless it has video input, i wonder if something based on animation and timing would work, as screenshots wouldn't clearly capture motion and response time would be too slow as well

So, a paywall is the simple solution