Count a group's website visits

[Impulse]

I use my webserver's logs to count visits to my website.The software "Webalizer 2" displays these data in plain form with some diagrams.But now I want to count visits by a special group of users separately. I have premium users and standard users. For premium users I want to have a separate statistics page so that I can see how many premium users' hits there are.How can I achieve that?In my PHP script files, I detect the status as follows:\[code\]<?phpif ($_SESSION['status'] == 'premium') { // do something here}?>\[/code\]The easiest way would - of course - be to have a MySQL update statement there to increment the premium users' counter.But that would also be a lot of database traffic. So I would prefer another solution.I thought I could show a 1x1 pixels .gif image to the premium users. Then I could check the webserver's statistics for the file "counter.gif". BUT: I guess the client will cache the graphics file so my results won't be correct, right?Do you have an idea how to implement such a counter?