What are some ways to identify a logged in user on the web?

Question

Here is the scenario:

There are 5 websites (different domain names) that need to share a session. I am using a bit of code on each site which returns a "blank.gif" image and at the same time sets the session (syncing it up to the current session). Each of the sites calls a session-img from each of the other sites. Also, all sites have access to the same database (where the session is stored). This works great on FF and Chrome, but not on IE (or Safari PC)...

I need to come up with an alternative method to keep a session active? The app is a small custom CMS, so really only 2-3 people will be using it.

I can probably identify user logins by IP and then continue to check for the IP accross all sites...

Is there something more granular such as a computer uuid that i can check for?

Answer 1

Anything that would make this possible without cooperation from users would be a bug in regard to user privacy and anonymity which would eventually get fixed. Websites aren't supposed to be able to find out what other sites a user has been to and what he has done there.