本篇文章是对php中的下载远程图片函数进行了详细的分析介绍，需要的朋友参考下

gurl 要下载的图片地址
$rfurl 来路。如果目标图像做了防盗链设置，可以绕过。
$filename 下载图片保存的文件名，相对路径，不要用realpath
$gcookie 调整cookie 伪造的cookie
$JumpCount 跳转计数
$maxtime 最大次数
调用方法：DownImageKeep(“http://www.baidu.com/img/baidu_jgylogo2.gif”,”http://baidu.com”,”a.gif”,”",0,10);

<?php
function DownImageKeep($gurl, $rfurl, $filename, $gcookie="", $JumpCount=0, $maxtime=30)
{
    $urlinfos = GetHostInfo($gurl);
    $ghost = trim($urlinfos['host']);
    if($ghost=='')
    {
        return FALSE;
    }
    $gquery = $urlinfos['query'];
    if($gcookie=="" && !empty($rfurl))
    {
        $gcookie = RefurlCookie($rfurl);
    }
    $sessionQuery = "GET $gquery HTTP/1.1\r\n";
    $sessionQuery .= "Host: $ghost\r\n";
    $sessionQuery .= "Referer: $rfurl\r\n";
    $sessionQuery .= "Accept: */*\r\n";
    $sessionQuery .= "User-Agent: Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)\r\n";
    if($gcookie!="" && !preg_match("/[\r\n]/", $gcookie))
    {
        $sessionQuery .= $gcookie."\r\n";
    }
    $sessionQuery .= "Connection: Keep-Alive\r\n\r\n";
    $errno = "";
    $errstr = "";
    $m_fp = fsockopen($ghost, 80, $errno, $errstr,10);
    fwrite($m_fp,$sessionQuery);
    $lnum = 0;
    //获取详细应答头
    $m_httphead = Array();
    $httpstas = explode(" ",fgets($m_fp,256));
    $m_httphead["http-edition"] = trim($httpstas[0]);
    $m_httphead["http-state"] = trim($httpstas[1]);
    while(!feof($m_fp))
    {
        $line = trim(fgets($m_fp,256));
        if($line == "" || $lnum>100)
        {
            break;
        }
        $hkey = "";
        $hvalue = "";
        $v = 0;
        for($i=0; $i<strlen($line); $i++)
        {
            if($v==1)
            {
                $hvalue .= $line[$i];
            }
            if($line[$i]==":")
            {
                $v = 1;
            }
            if($v==0)
            {
                $hkey .= $line[$i];
            }
        }
        $hkey = trim($hkey);
        if($hkey!="")
        {
            $m_httphead[strtolower($hkey)] = trim($hvalue);
        }
    }
    //分析返回记录
    if(preg_match("/^3/", $m_httphead["http-state"]))
    {
        if(isset($m_httphead["location"]) && $JumpCount<3)
        {
            $JumpCount++;
            DownImageKeep($gurl,$rfurl,$filename,$gcookie,$JumpCount);
        }
        else
        {
            return FALSE;
        }
    }
    if(!preg_match("/^2/", $m_httphead["http-state"]))
    {
        return FALSE;
    }
    if(!isset($m_httphead))
    {
        return FALSE;
    }
    $contentLength = $m_httphead['content-length'];
    //保存文件
    $fp = fopen($filename,"w") or die("写入文件：{$filename} 失败！");
    $i=0;
    $okdata = "";
    $starttime = time();
    while(!feof($m_fp))
    {
        $okdata .= fgetc($m_fp);
        $i++;
        //超时结束
        if(time()-$starttime>$maxtime)
        {
            break;
        }
        //到达指定大小结束
        if($i >= $contentLength)
        {
            break;
        }
    }
    if($okdata!="")
    {
        fwrite($fp,$okdata);
    }
    fclose($fp);
    if($okdata=="")
    {
        @unlink($filename);
        fclose($m_fp);
        return FALSE;
    }
    fclose($m_fp);
    return TRUE;
}
/**
 *  获得某页面返回的Cookie信息
 *
 * @access    public
 * @param     string  $gurl  调整地址
 * @return    string
 */
function RefurlCookie($gurl)
{
    global $gcookie,$lastRfurl;
    $gurl = trim($gurl);
    if(!empty($gcookie) && $lastRfurl==$gurl)
    {
        return $gcookie;
    }
    else
    {
        $lastRfurl=$gurl;
    }
    if(trim($gurl)=='')
    {
        return '';
    }
    $urlinfos = GetHostInfo($gurl);
    $ghost = $urlinfos['host'];
    $gquery = $urlinfos['query'];
    $sessionQuery = "GET $gquery HTTP/1.1\r\n";
    $sessionQuery .= "Host: $ghost\r\n";
    $sessionQuery .= "Accept: */*\r\n";
    $sessionQuery .= "User-Agent: Mozilla/4.0 (compatible; MSIE 5.00; Windows 98)\r\n";
    $sessionQuery .= "Connection: Close\r\n\r\n";
    $errno = "";
    $errstr = "";
    $m_fp = fsockopen($ghost, 80, $errno, $errstr,10) or die($ghost.'<br />');
    fwrite($m_fp,$sessionQuery);
    $lnum = 0;
    //获取详细应答头
    $gcookie = "";
    while(!feof($m_fp))
    {
        $line = trim(fgets($m_fp,256));
        if($line == "" || $lnum>100)
        {
            break;
        }
        else
        {
            if(preg_match("/^cookie/i", $line))
            {
                $gcookie = $line;
                break;
            }
        }
    }
    fclose($m_fp);
    return $gcookie;
}
/**
 *  获得网址的host和query部份
 *
 * @access    public
 * @param     string  $gurl  调整地址
 * @return    string
 */
function GetHostInfo($gurl)
{
    $gurl = preg_replace("/^http:\/\//i", "", trim($gurl));
    $garr['host'] = preg_replace("/\/(.*)$/i", "", $gurl);
    $garr['query'] = "/".preg_replace("/^([^\/]*)\//i", "", $gurl);
    return $garr;
}
?>