How to find MAC address of your visitor using PHP

MACaddressPHP

<?php 

ob_start(); 
system('ipconfig /all'); 
$mycom=ob_get_contents();
ob_clean(); 

$findme = "Physical"; 
$pmac = strpos($mycom, $findme); 
$mac=substr($mycom,($pmac+36),17); 

echo $mac; 

?>

It works on local server not on online server. Then what to do??
please help...

It only works as long as the data packet hasn't been passed on by the router, so it only works when your visitor is on the same network. Once the data is sent out, the MAC address in the data packets changes to that of the passing node and that continuously repeats as the packets hop through the internet. There is no way to recover the MAC address of the original host.