PHP image link rotation

The script is for my vbulletin forum in PHP which we can stick our affiliate banners with their links so that they rotate on refresh.

The code is as follows:

$total = "6"; //6 - change to how many images you have
$file_type = ".jpg"; //change to file type
$image_folder = "random"; //location of folder
$start = "1"; //which image you want to load first
$random = mt_rand($start, $total);
$image_name = $random . $file_type;
echo "\";