This is the Captcha library ported from Kohana 2.3.x to 3.x. Very little has changed API-wise, although there have been a few changes.
Instantiate a captcha:
$captcha = Captcha::instance();
Instantiate using your own config group (other than 'default'):
$captcha = Captcha::instance('myconfig');
Render a captcha:
Validate the captcha: