Error on Image caching

I try cache the image but it retun nothing
sometimes this error come out
"failed to open stream: HTTP request failed! HTTP/1.1 401 Access
Denied"

This is my code:
ob_start();

header("Content-Type: image/jpeg\n");

$image = 'http://www.roganjosh.co.uk/showPic.asp?picture=100';

readfile($image);
$data = ob_get_contents();
ob_end_clean();
echo $data;

or any of u can suggest other method to cache the image..
if the image generate dynamically ???

now i notice that the image have the query string (?)
any know how to cache image with querystirng