citywebshop_cms/imagesize.php

<?php

header("Content-Type: image/jpg");

$image = imagecreatefromjpeg($_REQUEST['image']);
$filename = $_REQUEST['image'];

if ($_REQUEST['w']!='' && $_REQUEST['h']!='') {
    $thumb_width = $_REQUEST['w'];
    $thumb_height = $_REQUEST['h'];
}
else {
    $thumb_width = 400;
    $thumb_height = 400;
}

$width = imagesx($image);
$height = imagesy($image);

$original_aspect = $width / $height;
$thumb_aspect = $thumb_width / $thumb_height;

if ( $original_aspect >= $thumb_aspect ) {
   $new_height = $thumb_height;
   $new_width = $width / ($height / $thumb_height);
}
else {
   $new_width = $thumb_width;
   $new_height = $height / ($width / $thumb_width);
}

$thumb = imagecreatetruecolor( $thumb_width, $thumb_height );

imagecopyresized($thumb,
                   $image,
                   0 - ($new_width - $thumb_width) / 2, 
                   0 - ($new_height - $thumb_height) / 2, 
                   0, 0,
                   $new_width, $new_height,
                   $width, $height);

imagejpeg($thumb,null,100);