Captcha Modules

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A captcha module (requires Q2A 1.5+) provides a web interface for verifying that a user is a human, rather than an automated script generating spam. The captcha should provide a challenge that is easy for humans but difficult for computers, such as reading some warped text or answering a common sense question.

The PHP class for a captcha module should contain the following functions (all except allow_captcha() are required):

  • allow_captcha(). If defined, this function allows the captcha module to indicate whether it is ready to be used. For example, if the captcha requires some settings which have not yet been defined, it can return false. If the function is not defined, Q2A assumes that the captcha module is always ready.
  • form_html(&$qa_content, $error). This function returns the HTML form to be displayed for the captcha challenge. You can use hidden fields in this form to provide any information required by validate_post() - see below. If $error is not null, it contains an error message that should be displayed with the captcha, as passed out previously by your validate_post() function. You can also inject elements (such as Javascript) into the global $qa_content array for the page - see qa-plugin/recaptcha-captcha/qa-recaptcha-captcha.php for an example, or ask here. Note that if a captcha is required in multiple places on a web page, Q2A will only call form_html() once, and will take care of moving the captcha around the page as appropriate. This means your captcha must continue to work even if it was moved inside the DOM.
  • validate_post(&$error). This function returns whether the user responded to the captcha correctly. The function should retrieve the necessary form fields from PHP’s $_POST array or Q2A’s qa_post_text() function, and then perform the appropriate verification. Return true if the verification succeeded, otherwise false. If verification failed, you should also set $error to a textual error message which will passed back to form_html() for display to the user.

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