PHP模拟POST传输图片问题

想通过模拟POST的方法传输图片，这是服务端
<?php

$URL = 'http://localhost/phppost/test2.php';

$img_file = 'D:\xampp\htdocs\byte.jpg';
$fp1 = fopen($img_file, 'rb');
$content = fread($fp1, filesize($img_file)); //二进制数据
$post_data['tu']=$content;

$referrer="";
$URL_Info=parse_url($URL);
if($referrer=="")
{
$referrer=$_SERVER["SCRIPT_URI"];
}
foreach ($post_data as $key=>$value)
{
$values[]="$key=".urlencode($value);
}
$data_string=implode($values);

if (!isset($URL_Info["port"])) {
$URL_Info["port"]=80;
$request.="POST ".$URL_Info["path"]." HTTP/1.1\n";
$request.="Host: ".$URL_Info["host"]."\n";
$request.="Referer: $referrer\n";
$request.="Content-type: application/x-www-form-urlencoded\n";

$request.="Content-length: ".strlen($data_string)."\n";
$request.="Connection: close\n";
$request.="\n";
$request.=$data_string."\n";
}

$fp = fsockopen($URL_Info["host"], $URL_Info["port"]);


fputs($fp, $request);
while(!feof($fp)) {

$result .= fgets($fp