Exactly, You're just a mod_rewrite away from serving a single gif under infinitely many names. All you have to do is include a unique name in every email, and t

Exactly, You're just a mod_rewrite away from serving a single gif under infinitely many names. All you have to do is include a unique name in every email, and then look through your log files to see if anyone came for that gif. Tracking pixels are a pretty ancient technique and for good reason. It's basically no effort at all to set up the basics, and only a tiny bit more effort to get fancy at it and stick the accesses in a database instead of in the server logs.