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This article is part of an on-going series of tutorials explaining how to use the
SixPack library. In this example, we show how to use the
CaptchaImage class to generate effective CAPTCHAs for your site.
About the SixPack Library
SixPack rapid development library is a collection of classes for rapid development on the .NET/Mono platform. It is released under the Limited General Public License 2.1 (LGPL) and is available through Google code.
Using the Code
This is an example of using the
CaptchaImage class in the
Typically, you would generate a random sequence of characters, store it in session, then use this class to serve the image from a handler.
On submit, you would then compare the value input by the user with the value in session.
Stating the obvious: do NOT use a parameter to pass the correct CAPTCHA value to the handler... that would make the CAPTCHA useless!
A not-so-obvious note: mono does not support the
WarpPath method in
System.Drawing that we use to scramble the text. The class works around this by distorting the image in other ways under Unix environments. This is not as effective as the
Win32 method, unfortunately.
In future versions of the library, we might create another
CaptchaImage class based on ImageMagick, so we can provide a consistent user experience on both platforms.
public static void Main(string args)
CaptchaImage captcha = new CaptchaImage
("foo-bar", 300, 100, "Times New Roman");
captcha.BackgroundDark = TangoPalette.SkyBlue1;
captcha.BackgroundLight = TangoPalette.SkyBlue3;
captcha.ForegroundDark = TangoPalette.SkyBlue2;
captcha.ForegroundLight = TangoPalette.SkyBlue1;
captcha.FontStyle = FontStyle.Italic;
Image image = captcha.Generate();
Bitmap bitmap = new Bitmap(image);
The result of this operation will be the following (under mono):
- 20th March, 2009: Initial post