Altcha.NET
Using a proof-of-work mechanic to prevent spam in .NET web applications.
Screenshot from an example project
ALTCHA is one of many CAPTCHA alternatives. Altcha.NET is a small library that implements the ALTCHA challenge. It can generate and validate self-hosted challenges. You can also use it together with ALTCHA’s own API to take advantage of their spam filter.
I wrote this library because I’m working on a self-hosted comment system. Comment systems need anti-spam measures. There are many CAPTCHA alternatives, but most of them rely on external services, or cost money. Because I want my comment system to be completely self-hosted, I don’t want to make exceptions for anti-spam mechanics.
ALTCHA is a relatively simple system that can be completely self-hosted. So I wrote this library to support as much of ALTCHA as it can without being dependent on web frameworks like ASP.NET. Because I had so much fun writing it, I implemented much more of ALTCHA than I actually need myself. So hopefully it’s useful to others too!