So you have an image, a link that surrounds it and you want to record whether a visitor clicks on it?
The easiest way is to make a link to a PHP page, e.g. referer.php. This page would take a link as argument and then increment the amount of clicks for that link in a database:
<a href='referer.php?link=http://www.mysite.com'><img src="http://www.mysite.com/banners/2-12/160x600_5.jpg" width='160' height='600' border='1' alt="Click to Visit" /></a>
And then in referer.php you retrieve the link using GET, increment a value in a table (something like 'referer_counter') with columns 'link' (string) and 'counter' (integer) that corresponds with the link and then automatically redirect (google how to do it) the visitor to the correct link.
PS: If it's a rotation banner, you need to change the href everytime a new image is loaded.
~G