Captcha

如何用 ASP.NET 實做簡單的圖片驗證機制(Captcha)
實作ASP.NET MVC CAPTCHA驗證碼機制
[Google/ASP.net] Google reCaptcha 免費驗證碼圖片套件教學
Custom reCaptcha Validation
Using reCAPTCHA with ASP.NET
Image Verification Code for Logging

FETCH! Retrieve data from a remote web server with one line of code (with MVC reCAPTCHA example)