Email experiments: filtering out external images

I had a realization the other day that, on almost every email in my inbox, my mail client has a "show external images" option. Most email I receive references externally loaded images via HTML. There are good reasons for this (not needing to send a copy of an image in every email on a newsletter) as well as nefarious reasons (the remote server can track where/when you load the image). So most mail…