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<sect1 id="zend.captcha.introduction">
    <title>Introduction</title>

    <para>
        <ulink url="http://en.wikipedia.org/wiki/Captcha">CAPTCHA</ulink>
        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.
    </para>

    <para>
        Captchas can take a variety of forms, including asking logic questions, presenting skewed
        fonts, and presenting multiple images and asking how they relate.
        <classname>Zend_Captcha</classname> aims to provide a variety of back ends that may be
        utilized either standalone or in conjunction with <classname>Zend_Form</classname>.
    </para>
</sect1>
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