From EFF's Web Bug FAQ(point 6),
What information is sent to a server when a Web Bug is viewed?
- The IP address of the computer that fetched the Web Bug
- The URL of the page that the Web Bug is located on
- The URL of the Web Bug image
- The time the Web Bug was viewed
- The type of browser that fetched the Web Bug image
- A previously set cookie value
I understand how (1), (3), (4), (5) can be fetched. Even (2) could be arranged by making sure that the pages that you want to track (which have the tracking pixels in them), have a one to one web bug url.
But what I clearly don't get is how would you get (6)? If you have a web bug on
trackee.com/page that makes a request to
tracker.com/pixel.gif, how can
tracker.com identify a cookie stored under the domain of
trackee.com? Is there something I am missing here?