SimpleCaptcha and Kaptcha

The images produced by these open source packages looks good enough. Both are very easy to setup.

SimpleCaptcha (http://simplecaptcha.sourceforge.net)

// build captcha
Captcha captcha = Captcha.Builder(200, 50)
            .addText()
            .gimp()
            .addBorder()
            .addBackground(new GradiatedBackgroundProducer())
            .build();

// write image
ImageIO.write(captcha.getImage(), "png", output);

Kaptcha (http://code.google.com/p/kaptcha)

    // configurations
    Properties prop = new Properties();
    prop.setProperty(Constants.KAPTCHA_NOISE_IMPL,
                     "com.google.code.kaptcha.impl.NoNoise");
    prop.setProperty(Constants.KAPTCHA_OBSCURIFICATOR_IMPL,
                     "com.google.code.kaptcha.impl.WaterRipple");

    // build captcha
    Config config =  new Config(prop);
    Producer producer = config.getProducerImpl();
    String text = producer.createText();

    // write image
    ImageIO.write(producer.createImage(text), "png", output);