I'm a founder in this space (www.roundtable.ai; YC S23)
Behavior is a big missing link. Many CAPTCHA services (including Google reCAPTCHA v3) claim to use behavioral analyses, but you can disprove this using Operator to fill out a form and see reCAPTCHA and other bot detection systems flag it as a human.
At Roundtable, we rely on first-order behavioral markers (keystroke, mouse, scroll, click) etc. When first-order are sufficiently spoofed, analyze higher-level cognitive traits (e.g. incongruent effect in Stroop)
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