PHP - Ayuda codigo QR PHP

<?php

/**

 * QR Code + Logo Generator

 *

 * http://labs.nticompassinc.com

 */

$data = isset($_GET['data']) ? $_GET['data'] : 'http://labs.nticompassinc.com';

$size = isset($_GET['size']) ? $_GET['size'] : '400x400';

$logo = isset($_GET['logo']) ? $_GET['logo'] : '';

header('Content-type: image/png');

// Get QR Code image from Google Chart API

// http://code.google.com/apis/chart/infographics/docs/qr_codes.html

$QR = imagecreatefrompng('https://chart.googleapis.com/chart?cht=qr&chld=H|1&chs='.$size.'&chl='.urlencode($data));

if($logo !== FALSE){

	$logo = imagecreatefromstring(file_get_contents($logo));

	$QR_width = imagesx($QR);

	$QR_height = imagesy($QR);

	$logo_width = imagesx($logo);

	$logo_height = imagesy($logo);

	// Scale logo to fit in the QR Code

	$logo_qr_width = $QR_width/3;

	$scale = $logo_width/$logo_qr_width;

	$logo_qr_height = $logo_height/$scale;

	imagecopyresampled($QR, $logo, $QR_width/3, $QR_height/3, 0, 0, $logo_qr_width, $logo_qr_height, $logo_width, $logo_height);

}

imagepng($QR);

imagedestroy($QR);

?>