OpenCaptcha is software that generates CAPTCHA images; examples are shown below.

OpenCaptcha is actively used by others, generating over 90,000 CAPTCHA images per month, as shown in the image below.

Interestingly, the software is based on code that is over 20 years old, initially published in 2004.

(https://web.archive.org/web/20241116012010/https://www.codeproject.com/Articles/5947/CAPTCHA-Image)

Since I wanted people to use my software, I made it free. I also created a documentation website (www.opencaptcha.io) that explains how to use it and provides examples.