The best open source alternative to reCAPTCHA is Cap Captcha. If that doesn't suit you, our users have ranked more than 25 alternatives to reCAPTCHA and ten of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to reCAPTCHA are Anubis, Procaptcha, ALTCHA and mosparo.
Lightweight, modern open-source CAPTCHA alternative designed using SHA-256 proof-of-work.
Cap Captcha is the most popular Self-Hosted alternative to reCAPTCHA.
Cap Captcha is the most popular Open Source & free alternative to reCAPTCHA.
Applies sha256 proof-of-work challenges to incoming HTTP requests, targeting AI crawlers, bots that ignore robots.txt, and automated scrapers, protecting server resources and preventing unwanted search engine indexing for privacy-focused sites.
I put this on my company page and now my colleagues think I'm into furries
Prosopo Procaptcha redefines user verification with a unique approach that emphasizes privacy and security. It's a pioneering solution designed to offer an alternative to conventional CAPTCHA systems that often compromise user privacy.
It works better, it costs less, it doesn't track your users, it has invisible challenges for humans stops bots. Need I say more?
Almost everyone thinks Procaptcha is a great reCAPTCHA alternative.
Procaptcha is the most popular SaaS alternative to reCAPTCHA.
ALTCHA is a privacy-first solution built to help developers and website owners stop bots, spam, and automated abuse — without making things harder for real users. It replaces traditional CAPTCHA systems with a smarter, quieter approach to verification and threat detection.
Its proof of work only - this is a delay mechanism only so I don't know why its in the "stop bots" category?
mosparo is the modern solution for protecting your online forms from spam. The protection method is quite simple: mosparo blocks spam using rules matching the form’s data. The detection method is comparable to an e-mail spam filter.
It is Free and Open Source. Inspectable.
conCaptcha is a self-hosted captcha which is faster, more user-friendly and more customizable than other captchas - available for PHP and ASP.NET websites. Users no longer have to read any annoying text images, solve difficult math equations or play any puzzle games.
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I tried cap captcha on my site and the bots just kept on spamming me.