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Captcha Operation - Zend_Captcha
All CAPTCHA adapter implement Zend_Captcha_Adapter, which looks like the following:
The name setter and getter are used to specify and retrieve the CAPTCHA identifier. getDecorator() can be used to specify a Zend_Form decorator either by name or returning an actual decorator object. The most interesting methods are generate() and render(). generate() is used to create the CAPTCHA token. This process typically will store the token in the session so that you may compare against it in subsequent requests. render() is used to render the information that represents the CAPTCHA, be it an image, a figlet, a logic problem, or some other CAPTCHA.
A typical use case might look like the following: