圈中裁剪图像(php)

<?php
error_reporting(E_ALL);
ini_set('display_errors','1');

$filename = "../../content/".base64_decode($_GET["file"]);


$ext = pathinfo($filename,PATHINFO_EXTENSION);

if ($ext=="jpg" || $ext=="jpeg") {
$image_s = imagecreatefromjpeg($filename);
} else if ($ext=="png") {
$image_s = imagecreatefrompng($filename);
}

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


$newwidth = 285;
$newheight = 232;

$image = imagecreatetruecolor($newwidth,$newheight);
imagealphablending($image,true);
imagecopyresampled($image,$image_s,$newwidth,$newheight,$width,$height);

// create masking
$mask = imagecreatetruecolor($width,$height);
$mask = imagecreatetruecolor($newwidth,$newheight);



$transparent = imagecolorallocate($mask,255,0);
imagecolortransparent($mask,$transparent);



imagefilledellipse($mask,$newwidth/2,$newheight/2,$transparent);



$red = imagecolorallocate($mask,0);
imagecopy($image,$mask,$newheight);
imagecolortransparent($image,$red);
imagefill($image,$red);

// output and free memory
header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
imagedestroy($mask);
?>

它在我的笔记本电脑上显示以下图像：
http://i.stack.imgur.com/Aai1r.png

这就是它在远程服务器上的显示方式：
http://i.stack.imgur.com/77fbV.png

你怎么看？有什么问题？