cagraham writes "In a seemingly minor update, Google announced that all Gmail images will now be cached on their own servers, before being displayed to users. This means that users won't have to click to download images in every email now — they'll just automatically be shown. For marketers, however, the change has serious implications. Because each user won't download the images from a third-party server, marketers won't be able to see open-rates, log IP addresses, or gather information on user location and browser type. Google says the changes are intended to enhance user privacy and security."
We warn the reader in advance that the proof presented here depends on a
clever but highly unmotivated trick.
-- Howard Anton, "Elementary Linear Algebra"