Hỏi về host resell

<?php
session_start();
create_image();
exit();
function create_image()
{
    $md5_hash = md5(rand(0,999));
    $security_code = substr($md5_hash, 15, 5);
    $_SESSION["security_code"] = md5($security_code);
    $width = 73;
    $height = 20;
    $image = ImageCreate($width, $height); 
    $white = ImageColorAllocate($image, 14, 59, 130);
    $black = ImageColorAllocate($image, 240, 254, 255);
    ImageFill($image, 0, 0, $black);
    ImageString($image, 5, 15, 2, $security_code, $white);
    header("Content-Type: image/jpeg");
    ImageJpeg($image);
    ImageDestroy($image);
}
?>

<?php
session_start();

// generate 5 digit random number
$rand = rand(10000, 99999);

// create the hash for the random number and put it in the session
$_SESSION['image_random_value'] = md5($rand);

// create the image
$image = imagecreate(50, 18);

// use white as the background image
$bgColor = imagecolorallocate ($image, 0x88, 0x00, 0x00);

// the text color is black
$textColor = imagecolorallocate ($image, 0xCC, 0XCC, 0xCC);

// write the random number
imagestring ($image, 4, 3, 1, $rand, $textColor);

// send several headers to make sure the image is not cached
// taken directly from the PHP Manual

// Date in the past
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");

// always modified
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

// HTTP/1.1
header("Cache-Control: no-store, no-cache, must-revalidate");
header("Cache-Control: post-check=0, pre-check=0", false);

// HTTP/1.0
header("Pragma: no-cache");


// send the content type header so the image is displayed properly
header('Content-type: image/jpeg');

// send the image to the browser
imagejpeg($image);

// destroy the image to free up the memory
imagedestroy($image);
?>