php生成缩略图

<?php
//image test
header("Content-type: image/jpeg");
$picfile='2.jpg';
$im=imagecreatefromjpeg($picfile);
$color=imagecolorallocate($im,255,255,255);
imagestring($im,1,5,5,"imbeded string",$color);
$filesize=getimagesize($picfile);

$output = imagecreatetruecolor(100,100);
if ( !$output ) {
error("Generate Error!");
return false;
}
imagecopyresampled($output,$im,0,0,0,0,100,100,$filesize[0],$filesize[1]);
$new='img/'.uniqid('s').$picfile;
if(imagejpeg($output,$new))
echo "okay!";
?>