Option for displaying blank page on wrong response, to consume less resources

create a variable captcha_errorpage o some else. I've used the http error 503, but this is my humble choice.

// $Id: captcha.module,v 1.42.2.24 2007/08/24 03:16:29 wundo Exp $
function captcha_validate($form_values) {
  // Get answer and preprocess if needed
  $captcha_response = $form_values['#post']['captcha_response'];
  $validationdata = $form_values['validationdata']['#value'];
  if ($validationdata['preprocess']) {
    $captcha_response = module_invoke($validationdata['module'], 'captcha', 'preprocess', $validationdata['type'], $captcha_response);
  }
  $form_id = $validationdata['form_id'];
  $captcha_errorpage = variable_get('captcha_errorpage', 'Blank');
  $captcha_token = $form_values['#post']['captcha_token'];
  // Check if captcha_token exists
  if (!isset($_SESSION['captcha'][$form_id][$captcha_token])) {
    if ($captcha_errorpage == 'Blank'){
      @header('HTTP/1.0 503 Service unavailable');
      print t('Invalid captcha token.');
    }
    else 
      form_set_error('captcha_token', t('Invalid captcha token.'));
  }
  // Check answer
  if ($captcha_response === $_SESSION['captcha'][$form_id][$captcha_token]) {
    $_SESSION['captcha'][$form_id]['success'] = TRUE;
  }
  else {
    if ($captcha_errorpage == 'Blank'){
      @header('HTTP/1.0 503 Service unavailable');
      print t('The answer you entered for the captcha challenge was not correct.');
    }
    else 
      form_set_error('captcha_response', t('The answer you entered for the captcha challenge was not correct.'));
  }

  // Unset the solution to prevent reuse of the same captcha solution
  // by a spammer that repeats posting a form without requesting
  // (and thus rendering) a new form. Note that a new captcha solution is only
  // set at the pre_render phase.
  unset($_SESSION['captcha'][$form_id][$captcha_token]);
}