If you want to try different Images/Banners with tracking code:
Code:
<?php
$rand = rand(1, 8); //example for 8 different images/banners
$ads = "<a href=\"AFFLINK?WM-ID&CAMPAIGN=CampaignName$rand\" title=\"title-text\" rel=\"nofollow\"><img src=\"/path-to-image/Image-$rand.gif\" alt=\"alt-text\" /></a>";
echo $ads;
?>
You should name the images/banners like:
Image-1
Image-2
Image-3
...
Image-8