Alternatives / reCAPTCHA
Looking for an open source reCAPTCHA alternative? We compared 6 CAPTCHA systems by license, proof-of-work design, privacy, and self-hosting. Most replace image puzzles with proof-of-work challenges, and three of them use licenses that restrict commercial use or keep parts closed.
Written by Maxime DERAME
Last updated:
| Alternative | Best for | License |
|---|---|---|
| Cap | Lightweight proof-of-work CAPTCHA under Apache-2.0 | Apache-2.0 |
| ALTCHA | Proof-of-work with optional paid features | MIT core + paid Pro |
| mCaptcha | Self-hosted proof-of-work CAPTCHA (slow development) | AGPL-3.0 core, permissive client libraries |
| Procaptcha | Blockchain-based bot defense | Apache-2.0 |
| Private Captcha | Privacy-first CAPTCHA (non-commercial self-hosting) | PolyForm Noncommercial (community edition) |
| Friendly Captcha | Invisible proof-of-work (closed backend) | Closed backend; Lite server non-commercial source available |
We looked for tools that overlap with reCAPTCHA's core: protecting forms from bots without relying on a large tracking provider. We verified each project's license, recent activity, stars, and self-hosting in its repository. We flag licenses that restrict commercial use and products whose backend is closed, because licensing matters a lot for something you embed in production. See our methodology for the full criteria.
Proof-of-work CAPTCHAs make bots spend computing time per request, which stops simple spam but not determined attackers with large resources. They avoid tracking and puzzles, but you should test them against the bots you face and combine them with rate limiting and other checks.
Cap is Apache-2.0, ALTCHA's core is MIT, and Procaptcha is Apache-2.0. mCaptcha's core is AGPL-3.0 with client libraries under more permissive licenses. Private Captcha's community edition uses the PolyForm Noncommercial License, so commercial use needs a commercial license. Friendly Captcha's backend is closed source, and its Lite server is a non-commercial source-available license.
Cap, ALTCHA, and mCaptcha are the closest drop-in replacements as proof-of-work widgets that run in the background. Private Captcha and Friendly Captcha are privacy-focused hosted services with paid plans, and Procaptcha describes a blockchain-based system with broad marketing claims.
ALTCHA's advanced features, such as spam filtering and analytics, need its Pro plan, starting at €9 a month. Private Captcha's paid service starts at €9 a month for 10,000 requests and is hosted in the EU. Friendly Captcha pricing ranges from free non-commercial use to enterprise plans.
Cap, ALTCHA, Procaptcha, and Private Captcha had commits within days or weeks of this update. mCaptcha's last commit was in October 2025, and Friendly Captcha's Lite server last changed in February 2024, so both are effectively stalled.
reCAPTCHA is a proprietary Google service that collects data about visitors and can add friction with image challenges, with usage beyond the free quota billed through Google Cloud. Alternatives replace tracking with proof-of-work challenges, keep data private, and in some cases can be self-hosted, at the cost of weaker defense against sophisticated bots than Google's network-wide signals.
Cap is an Apache-2.0 lightweight CAPTCHA that uses SHA-256 proof-of-work, with no visual puzzles and no telemetry. It is not related to the Cap screen recorder.
Pricing: Free and open source.
ALTCHA is a proof-of-work CAPTCHA alternative that also offers spam filtering, analytics, and form tools. The open-source widget is MIT-licensed with a free tier, while advanced features require the Pro plan starting at €9 a month.
Pricing: Free open-source tier; Pro starts at €9 a month.
mCaptcha is a proof-of-work CAPTCHA that runs in the background and is presented as a drop-in reCAPTCHA replacement, self-hosted. The core is AGPL-3.0, with client libraries under more permissive licenses. Its last commit was in October 2025, so development has slowed.
Pricing: Free and open source.
Procaptcha is a CAPTCHA and bot-defense system from Prosopo, described as blockchain-based, with an Apache-2.0 repository. Its security and bot-resistance claims are marketing language, and the project gives few details on self-hosting.
Pricing: Free tiers and paid plans; check the website.
Private Captcha is a privacy-focused CAPTCHA that works without puzzles, tracking, or cookies, hosted in the EU. The community edition is distributed under the PolyForm Noncommercial License, so self-hosting is allowed only for non-commercial use, and commercial licenses are available. The paid service starts at €9 a month for 10,000 requests.
Pricing: Paid service from €9 a month; commercial self-hosting needs a commercial license.
Friendly Captcha is a proof-of-work CAPTCHA that runs invisibly and emphasizes privacy and accessibility. Its backend is closed source, and a Lite server for self-hosting is available under a non-commercial source-available license (Apache 2.0 with a Commons Attribution Clause), last updated in February 2024. Pricing ranges from free non-commercial use to enterprise plans.
Pricing: Free for non-commercial use; paid plans for businesses.
| Alternative | Type | License | Self-hosted | Best for |
|---|---|---|---|---|
| Cap | Proof-of-work CAPTCHA | Apache-2.0 | Yes | Lightweight, no tracking |
| ALTCHA | Proof-of-work CAPTCHA | MIT core + paid Pro | Yes | Spam filtering add-ons |
| mCaptcha | Proof-of-work CAPTCHA | AGPL-3.0 | Yes | Self-hosting |
| Procaptcha | Decentralized CAPTCHA | Apache-2.0 | Partly | Bot resistance |
| Private Captcha | Privacy-first CAPTCHA | PolyForm Noncommercial | Non-commercial only | EU privacy |
| Friendly Captcha | Invisible CAPTCHA | Closed backend; Lite server non-commercial | Lite server only | Invisible challenges |
Want a lightweight, tracking-free replacement
Cap is an Apache-2.0 proof-of-work CAPTCHA with no puzzles and no telemetry.
Want proof-of-work with optional extra tools
ALTCHA offers a free open-source tier and paid Pro features such as spam filtering and analytics.
Want to run it all on your own server
mCaptcha is a self-hosted AGPL-3.0 proof-of-work CAPTCHA, though its development has slowed.
Want an EU-hosted, privacy-first service
Private Captcha works without puzzles, tracking, or cookies, but self-hosting is limited to non-commercial use.