If I put an image in a post in this thread, then I can get a list of the IPs of the people who have viewed the thread. Cross refer a few threads, and I can probably isolate your individual IP.
is it really possible to place an image - even an invisible image - that works like the traking things that are sent via e-mail? the images that services like mailchimp uses.
edit. sorry, i should have read the second page too before asking this question.