<?php
if (!isset($_SERVER['PHP_AUTH_USER'])) {
    header('WWW-Authenticate: Basic realm="Stack Overflow"');
    header('HTTP/1.0 401 Unauthorized');
    header("Content-type: image/jpg");
       echo file_get_contents("hacked.jpg");
    exit;
} else {
    header("Content-type: image/gif");
       echo file_get_contents("block.gif");
}
?>