/**
  * Generate a captcha, write the characters into $_SESSION['captcha'] and returns a real image which will be used
  * like this: <img src="......./login/showCaptcha" />
  * IMPORTANT: As this action is called via <img ...> AFTER the real application has finished executing (!), the
  * SESSION["captcha"] has no content when the application is loaded. The SESSION["captcha"] gets filled at the
  * moment the end-user requests the <img .. >
  * Maybe refactor this sometime.
  */
 public function showCaptcha()
 {
     CaptchaModel::generateAndShowCaptcha();
 }