Merge pull request #449 from ovx/patch-1

Add Altcha.org to Captchas

README.md

@@ -280,6 +280,7 @@ Google captchas use cookies to track users and rank their IPs.
 - Google reCAPTCHA [![](https://shields.tosdr.org/en_217.svg)](https://tosdr.org/en/service/217)
 
 <img width="16" src="misc/check.png"> </img>  **Instead use**
+- [Altcha.org](https://altcha.org) - Free, open-source and self-hosted CAPTCHA alternative using proof-of-work mechanism.
 - [hCaptcha](https://www.hcaptcha.com/) - Privacy-first CAPTCHA for web, mobile, and more.
 - [mCaptcha](http://mcaptcha.org/) ([repo](https://github.com/mCaptcha/mCaptcha)) - An open-source CAPTCHA system with seamless UX.  mCaptcha uses SHA256 based proof-of-work (PoW) to rate limit users.
 - [OOPSpam](https://www.oopspam.com/) - No-captcha, privacy-friendly anti-spam, anti-bot API. Requires no personal data for detection. Supports popular platforms like WordPress. Privacy commitment in their mission statement.