NanoCaptcha

What is this?

NanoCaptcha is a Java library for generating image and audio CAPTCHAs. NanoCaptcha is intended to be:

• Self-contained: no network API hits to any external services.

• Minimally-dependent: using NanoCaptcha should not involve pulling in a plethora of JARs, and ideally none at all.

Getting started

You can build a minimal image CAPTCHA very easily:

ImageCaptcha imageCaptcha = ImageCaptcha.create();

This creates a 200 x 50 pixel image and adds five random characters from the Latin alphabet. The getImage() method returns the image as a BufferedImage object. isCorrect(String) will verify the supplied string against the text content of the image. If you need the text content itself, call getContent(). Image CAPTCHAs can be further customised by:

• Using different ContentProducers (e.g., ChineseContentProducer).
• Supplying your own Colors and Fonts.
• Adding noise using a NoiseProducer.
• Adding various ImageFilters.
• Adding a background or a border.

To create a custom CAPTCHA, you can use an ImageCaptcha.Builder, e.g.:

ImageCaptcha imageCaptcha = new ImageCaptcha.Builder(400, 100)
    .addContent(new LatinContentProducer(7),
        new DefaultWordRenderer.Builder()
            .randomColor(Color.BLACK, Color.BLUE, Color.CYAN, Color.RED)
            .build())
    .addBackground(new GradiatedBackgroundProducer())
    .addNoise(new CurvedLineNoiseProducer())
    .build();

Building a minimal audio CAPTCHA is just as easy:

AudioCaptcha audioCaptcha = AudioCaptcha.create();

This creates a CAPTCHA with an audio clip containing five numbers read out in English (unless the default Locale has been changed). To customise your CAPTCHA, you can use AudioCaptcha.Builder.

There is support for different languages. (Currently English and German are supported.) You can set the system property net.logicsquad.nanocaptcha.audio.producer.RandomNumberVoiceProducer.defaultLanguage to a 2-digit code for a supported language, e.g., de, and the Builder above will return German digit vocalizations. Alternatively, you can supply a RandomNumberVoiceProducer explicitly:

AudioCaptcha audioCaptcha = new AudioCaptcha.Builder()
    .addContent()
    .addVoice(new RandomNumberVoiceProducer(Locale.GERMAN))
    .build();

You can even mix languages by calling addVoice(Locale) more than once.

As with image CAPTCHAs, these can be further customised by:

• Adding background noise with a NoiseProducer.

Playing the audio is probably application-dependent, but the following snippet will play the clip locally:

Clip clip = AudioSystem.getClip();
clip.open(audioCaptcha.getAudio().getAudioInputStream());
clip.start();
Thread.sleep(10000);

(The call to Thread.sleep() is simply to keep the JVM alive long enough to play the clip.)

Using NanoCaptcha

You can use NanoCaptcha in your projects by including it as a Maven dependency:

<dependency>
  <groupId>net.logicsquad</groupId>
  <artifactId>nanocaptcha</artifactId>
  <version>2.1</version>
</dependency>

Contributing

By all means, open issue tickets and pull requests if you have something to contribute.

References

NanoCaptcha is based on SimpleCaptcha, and incorporates code from JH Labs Java Image Filters.