Correct me if I'm talking directly from my rear end: For that scenario, Google could ignore the arguments and just request the file. However, I'm not sure I ge

Correct me if I'm talking directly from my rear end: For that scenario, Google could ignore the arguments and just request the file. However, I'm not sure I get Google's implementation of the proxy, but if the images are grabbed only when the email is read, it's easy to track by adding a hash to the filename itself. So, in the email company's server, they'd have a canonical file, for instance, acme-co/dec2013news/img53.jpg. For each subscriber, they'd have something like a symbolic link to img53.jpg specific to the subscriber, for instance img53-5baa61e4c9b93f3f0682250b6cf8331b7ee68fd8.jpg. EDIT: Checked a newsletter's source and that's what they already do. Since I don't deal with email marketing much, I honestly had no idea.