I would like to report some additional findings:
One way to track a user is to use graphic files as a substitute for
cookies. An image is created on a server with an identification number
encoded as color information. This image will be saved on a user’s
computer in the browser cache. When this user visits the website
again,
the locally stored image file will be opened and analyzed. The stored
color information will be sent back to the server to make tracking
possible. Since graphics are stored in a different location than
cookies, they aren’t deleted when you clear your cookies. Other
techniques include HTTP E-Tags, Flash cookies or web storage.
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