Generate QR code with custom logo

index.php

<?php
/**
 * QR Code + Logo Generator
 *
 * http://labs.nticompassinc.com
 */
$data = isset($_GET['data']) ? $_GET['data'] : 'https://tunlookup.com/';
$size = isset($_GET['size']) ? $_GET['size'] : '200x200';
$logo = isset($_GET['logo']) ? $_GET['logo'] : FALSE;
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);

Where i'll insert this code?