I am a newbie to banner advertising and I'm getting pretty confused trying to record the number of banner impressions on my site. I check the logs counting the number of times banner.gif has been requested but that figure is way lower than the number of pages that I know have been viewed carrying that banner. I guess this is probably because I'm using just the one banner throughout the site at the moment and so it's getting cached on first view. How are you supposed to measure banner impressions? Do you have to disable cacheing or something?
If i were you I would use a free ad script like phpads new very easy to track impressions and clicks and will rotate multiple banners
If You do not want to use a prebuild system You can write a little .php scritp that would count impressions, and give out the image adding some headers to stop caching of the image banner. In this manner you can also change the banner randomly at every request.