FCaptcha – A modern CAPTCHA system designed to detect everything

FCaptcha is an open-source CAPTCHA system that uses multiple detection methods to block traditional bots, automation frameworks, and modern vision-based AI agents that use screenshot-to-API workflows. The system combines proof-of-work challenges, behavioral analysis of 40+ signals including micro-tremor and mouse movements, environmental detection of headless browsers, and temporal pattern analysis to identify automated traffic. Unlike traditional CAPTCHAs, it offers both single-click and invisible modes while maintaining privacy through session-scoped fingerprinting without cross-site tracking.