CAPTCHA in java [duplicate]

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I wanna give a shot at developing a secure login system in Java. How should I implement CAPTCHA using Java?

The three CAPTCHA libraries I've used for Java are:

JCaptcha - This is the most configurable of the three, and pretty well documented. But we can't seem to get this to look right, no matter what. It also does audio and other unconventional CAPTCHAs
JCaptcha example http://jcaptcha.sourceforge.net/samples/SimpleListImageCaptchaEngineCaptcha_0.jpg
http://jcaptcha.sourceforge.net/
SimpleCaptcha - This is reasonably configurable, and pretty well documented. I like the way this looks, but some people have trouble reading it.
SimpleCaptcha example http://simplecaptcha.sourceforge.net/images/Captcha.jpg
http://simplecaptcha.sourceforge.net/
icaptcha - This is pretty poorly documented, but shouldn't be too hard to figure out from the examples. In our tests, we found this to be more readable than the other two (can be a good thing or a bad thing, depending on your target audience)
icaptcha example http://icaptcha.googlecode.com/files/2_img_test.jpg
http://code.google.com/p/icaptcha/

Our apps are Spring MVC based, and it was really easy to integrate these.

We just went with what looked best to us (icaptcha).

I know it's an old question, but I would like to recommend Cage.

open source, Apache v2 licensed so it can be used in enterprise/proprietary projects too
supports maven (available from the central maven repository)
fast (on the test pc 3-5 msec / image)
small (a single, small jar, no external dependencies, only Java 1.5 or newer is needed)