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();
	}