Using awstats to monitor/graph visitors on a server that only serves images?

I have an apache webserver that serves up images. Lots of machine generated images (i.e. not static files). It doesn't serve any serious amount of html etc. files. A user might request many images one after the other, which is essentially a form of "visitor" to the web site.

I want to use awstats to graph and show details about how busy the webserver is. I've set it up, and it's showing some data (amount of hits, bandwidth), however it has tiny numbers for "visitors". It looks like awstats doesn't, by default, count png files as something that "visitors" would do.

How can I make awstats treat hits to an image as something that a "visitor" would do, so that it will show better, more accurate, figures for "number of visitors"?