Online Status Indicator

Hey guys

I've been trying to come up with a way to figure out which image the server sends to the client after its figured out the status of the request.

Say that someone uses OSI to show his msn messenger status, someone loads his page, a request is sent to the OSI server and the OSI server sends back the correct image data (online or offline). I want to find out what the OSI server sends back so that I can alter the alt or title values for the image on onload so that it says something like "User is online" in the alt text.
ex. <img src="www.osiserver.com/msn/username@hotmail.com" alt="blah" onload="this.alt='response from server';">

Is there a procedure for this already that I've missed or has someone come up with a way?

Regards
Jesper