.. _zend.captcha.introduction: Introduction ============ `CAPTCHA`_ stands for "Completely Automated Public Turing test to tell Computers and Humans Apart"; it is used as a challenge-response to ensure that the individual submitting information is a human and not an automated process. Typically, a captcha is used with form submissions where authenticated users are not necessary, but you want to prevent spam submissions. Captchas can take a variety of forms, including asking logic questions, presenting skewed fonts, and presenting multiple images and asking how they relate. The ``Zend\Captcha`` component aims to provide a variety of back ends that may be utilized either standalone or in conjunction with the ``Zend\Form`` component. .. _`CAPTCHA`: http://en.wikipedia.org/wiki/Captcha