[tus89]

Right. I somehow interpreted it to mean a pixel in an existing image on the email, not some random pixel image.

Which makes me wonder why they don't just embed normal images that the user would see, but add something to the href that the server can interpret as a unique id. Either way, email clients that block images will break the technique.

[anewone]

There are certainly companies doing this already. The only advantage of a tracking pixel is if your email content doesn't have any images already. And I guess it sounds scarier for a headline.