Start the Session First thing right when the person enters your site
<?
session_start();
?>
then make an array and store it in the session for $visited_ids = array();
If you have a Nissan Xterra:
when the visitor goes to the xterra start the session on the Xterra Page, and then
array_push($visited_ids, Xterra);
session_register("visited_ids");
go to Next Picture: Ford Contour
on that page:
<?
session_start();
array_push($visited_ids, contour);
session_register("visted_ids");
?>
every car, do this, and keep the track right.
and then you can tell how many cars the visitor saw. And: if they see the same car twice, just make sure you're able to remove duplicate entries from the stored array.
Craig