I would like to find out how to call a banner using a normal url like they do at linkshare.com. They have a banner rotator with a code looking something like this...

<img src="http://ad.linksynergy.com/fs-bin/show?id=hqgqIxbBRRk&bids=30563&gridnum=-1&catid=-1&subid=0">

... This url calls a random banner from whatever merchant the the bids number belongs to. Could someone please tell me how this works? Does the url just pick a random banner and send the url for the banner or what?