code: static public function ping(\Base $f3, $params) {
  		$hash = $params['hash'];
  		// trigger ping event
  		if ($f3->exists('mailer.on.ping',$ping_handler))
  			$f3->call($ping_handler,array($hash));
  		$img = new \Image();
  		// 1x1 transparent 8bit PNG
  		$img->load(base64_decode('iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMA'.
  			'AAAl21bKAAAABGdBTUEAALGPC/xhBQAAAANQTFRFAAAAp3o92gAAAAF0U'.
  			'k5TAEDm2GYAAAAKSURBVAjXY2AAAAACAAHiIbwzAAAAAElFTkSuQmCC'));
  		$img->render();
  	}
docs: receive and proceed message ping
  @param Base $f3
  @param $params