// Check the recaptcha on WordPress MU
function check_recaptcha_wpmu($result) {
   global $_POST, $recaptcha_opt;

   // must make a check here, otherwise the wp-admin/user-new.php script will keep trying to call
   // this function despite not having called do_action('signup_extra_fields'), so the recaptcha
   // field was never shown. this way it won't validate if it's called in the admin interface
   if (!is_admin()) {
         // It's blogname in 2.6, blog_id prior to that
      if (isset($_POST['blog_id']) || isset($_POST['blogname']))
        return $result;

      // no text entered
      if (empty($_POST['recaptcha_response_field']) || $_POST['recaptcha_response_field'] == '') {
        $result['errors']->add('blank_captcha', $recaptcha_opt['error_blank']);
        return $result;
      }

      $response = recaptcha_check_answer($recaptcha_opt['privkey'],
         $_SERVER['REMOTE_ADDR'],
         $_POST['recaptcha_challenge_field'],
         $_POST['recaptcha_response_field'] );

      // incorrect CAPTCHA
      if (!$response->is_valid)
        if ($response->error == 'incorrect-captcha-sol') {
            $result['errors']->add('captcha_wrong', $recaptcha_opt['error_incorrect']);
            echo "<div class=\"error\">". $recaptcha_opt['error_incorrect'] . "</div>";
        }
   }

   return $result;
}