Here is the code:
<?php
if (isset($_GET['img'])){
if (file_exists($_GET['img'])){
ignore_user_abort(true);
set_time_limit(120);
ini_set('memory_limit', '512M');
$src_size = getimagesize($_GET['img']);
if ($src_size === false){
die('Image does not exsist.');
}
$thumb_width = 250;
$thumb_height = 250;
if ($src_size['mime'] === 'image/jpeg'){
$src = imagecreatefromjpeg($_GET['img']);
}else if ($src_size['mime'] === 'image/png'){
$src = imagecreatefrompng($_GET['img']);
}else if ($src_size['mime'] === 'image/gif'){
$src = imagecreatefromgif($_GET['img']);
}
$src_aspect = round(($src_size[0] / $src_size[1]), 1);
$thumb_aspect = round(($thumb_width / $thumb_height), 1);
if ($src_aspect < $thumb_aspect){
// higher
$new_size = array($thumb_width, ($thumb_width / $src_size[0]) * $src_size[1]);
$src_pos = array(0, (($new_size[1] - $thumb_height) * ($src_size[1] / $new_size[1])) / 2);
}else if ($src_aspect > $thumb_aspect){
//wider
$new_size = array(($thumb_width / $src_size[1]) * $src_size[0], $thumb_height);
$src_pos = array((($new_size[0] - $thumb_width) * ($src_size[0] / $new_size[0])) / 2, 0);
}else{
//Same shape
$new_size = array($thumb_width, $thumb_height);
$src_pos = array(0, 0);
}
if ($new_size[0] < 1) $new_size[0] = 1;
if ($new_size[1] < 1) $new_size[1] = 1;
$thumb = imagecreatetruecolor($thumb_width, $thumb_height);
imagecopyresampled($thumb, $src, 0, 0, $src_pos[0], $src_pos[1], $new_size[0], $new_size[1], $src_size[0], $src_size[1]);
if ($src_size['mime'] === 'image/jpeg'){
imagejpeg($thumb, "thumbs/{$GET['img']}");
}else if ($src_size['mime'] === 'image/png'){
imagepng($thumb, "thumbs/{$GET['img']}");
}else if ($src_size['mime'] === 'image/gif'){
imagegif($thumb, "thumbs/{$GET['img']}");
}
header("Location: thumbs/{$_GET['img']}");
}
die();
}
if (is_dir('thumbs') === false){
mkdir('thumbs', 0744);
}
$images = glob('*.{jpg,jpeg,png,gif}', GLOB_BRACE);
?>
<html>
<head>
<title>Image Gallery</title>
</head>
<body>
<div>
<?php
foreach ($images as $image){
if (file_exists("thumbs/{$image}")){
echo "<a href=\"{$image}\"><img src=\"thumbs/{$image}\" alt=\"{$image}\" /></a>";
}else{
echo "<a href=\"{$image}\"><img src=\"?img={$image}\" alt=\"{$image}\" /></a>";
}
}
?>
</div>
</body>
</html>
I tried this on a local server and my web server but both had the same problem http://epic300.net/php/image_gallery/ 
Could anyone tell me what the problem is and hopefully how to fix it?
