Preventing Spam With An ASP.NET CAPTCHA Control

A CAPTCHA image displays text that is readable to humans, but not to computers. The concept is useful because it provides a means to filter out automated programs while allowing real users to pass through. Bots for example, which spam comments on weblogs and other dynamic websites, are a fairly pervasive problem and even a regularly new and low traffic blog like this was getting dozens of spam comments every day. CAPTCHA is a means to stop them while still allowing real users to post.

CaptchaControl is an ASP.NET server control that is designed to start working by just being dropping onto the page, without any modification. This version is based off Michael Trefry’s implementation, which is in turn based off Dan Burke’s. James' update fixes a couple of issues around storing the code in a browser cookie and adds features like client validation.

The source and dll for the project can be downloaded here: CaptchaControl.zip