Way to detect when a player logs off?

[Gunderak]

I have detection for when players log in but not off.
Basically I have coded my own playercount using PHP.
It uses a static image and adds text to it dynamically when players log on.
If no one logs on it updates every 5 minutes by requesturl.
Anyway here is the image for anyone that's interested.
I might release the source if people want it.
Also is there a way to detect when RC players log on?

http://wr3ckless.net/text/playercount.png