//判断防盗链域名
<?php
define('REFERER_URL', '');
function is_referer(){
    //没有设置防盗链
    if(REFERER_URL=='' || (empty($_SERVER['HTTP_REFERER']) && REFERER_ID==1)) return true; 
    //获取来路域名
    $uriarr = parse_url($_SERVER['HTTP_REFERER']);
    $host = $uriarr['host'];
    $ymarr = explode("|",REFERER_URL);
    if(in_array($host,$ymarr)){
        return true;
    }
    return false;
}

使用方法

//防盗链
if(!is_referer(REFERER_URL)){
    echo '非法访问，403~!';exit;
}