<?php
$thumbfile = "./guest_upload2/thumb/".$_FILES['userfile']['name'];
$uploadfile = $_FILES['userfile']['tmp_name'];
//Create thumb 
$width=500;
$height=500;
$size=GetImageSize($_FILES['userfile']['tmp_name']);
if($size[2]==1)
$im_in=imagecreatefromgif($uploadfile);
if($size[2]==2)
$im_in=imagecreatefromjpeg($uploadfile);
if($size[2]==3)
$im_in=imagecreatefrompng($uploadfile);
$im_out=ImageCreateTrueColor($width,$height);
/*ImageCopyResized*/
imagecopyresampled($im_out,$im_in,0,0,0,0,$width,$height,$size[0],$size[1]);
Imagejpeg($im_out,$thumbfile);
chmod($thumbfile,0777);
ImageDestroy($im_in);
ImageDestroy($im_out);
?>
压缩后的文件大小你自己加上判断.