Run Time Image Thumbnail

This code can be used to create Dynamic Image thumbnails on the fly
i.e. You need not to bother about the actual image size while uploading. Just show the desired scaled image anywhere on your website. Same image may need to display in different size on different web-page.

/********** (thumb.php) ****************/
$img=$_GET['img']; $w=$_GET['w']; $h=$_GET['h'];
if(!defined('DIR_CACHE'))
define('DIR_CACHE', './image_cache/');

if (!Is_Dir(DIR_CACHE))
mkdir(DIR_CACHE, 0777);

#IMAGE RESIZE AND SAVE TO FIT IN $new_width x $new_height
if (file_exists($img))
{
$thumb=strtolower(preg_replace('/\W/is', "_", "$img $w $h"));
$changed=0;

if(!is_file($img))
$img = "images/product-image.jpg";

if (file_exists($img) && file_exists(DIR_CACHE.$thumb))
{
$mtime1=filemtime(DIR_CACHE.$thumb);
$mtime2=filemtime($img);
if ($mtime2 > $mtime1)
$changed=1;
}
elseif (!file_exists(DIR_CACHE.$thumb))
$changed=1;

if ($changed)
{
$filename=$img;
$new_width=(int)@$w;
$new_height=(int)@$h;
$lst=GetImageSize($filename);
$image_width=$lst[0];
$image_height=$lst[1];
$image_format=$lst[2];

if ($image_format==1)
$old_image=imagecreatefromgif($filename);
elseif ($image_format==2)
$old_image=imagecreatefromjpeg($filename);
elseif ($image_format==3)
$old_image=imagecreatefrompng($filename);
else
exit;

if (($new_width!=0) && ($new_width < $image_width))
{
$image_height=(int)($image_height*($new_width/$image_width));
$image_width=$new_width;
}

if (($new_height!=0) && ($new_height < $image_height))
{
$image_width=(int)($image_width*($new_height/$image_height));
$image_height=$new_height;
}

$new_image=ImageCreateTrueColor($image_width, $image_height);
$white = ImageCopyResampled($new_image, $old_image, 0, 0, 0, 0, $image_width, $image_height, imageSX($old_image), imageSY($old_image));
#ImageFill($new_image, 0, 0, $white);
imageJpeg($new_image, DIR_CACHE.$thumb);
}

header("Content-type:image/jpeg");
readfile(DIR_CACHE.$thumb);
}
/********** CODE END ****************/

Here is the example use
< img src="thumb.php?img=image1.jpg?w=150&h=100" >

Tricky & nice :
If a thumbnail of a particular size of an image is created, script will not create the dynamic thumbnail again. It will pick that thumb from image_cache folder, if already exists.

note: "image_cache" folder requires 777 permission