Like most of the problems EU has tried (and failed) to solve with legislation, like cookie laws, this is an issue that is already entirely solved by the client. If you don't like having external images in your emails, most clients these days support turning it off.
Whether it's a header image or a "spy pixel", both of these things can be used to track you. Therefore the solution is to disable it entirely if you do not like being tracked.
> this is an issue that is already entirely solved by the client
No it isn't.
What if I want to see the images in an email newsletter, but don't want to be tracked? The client can't give me a button "open images except tracking pixels" because it doesn't have enough information to know the difference.
>What if I want to see the images in an email newsletter, but don't want to be tracked?
That would be nice, but as I already wrote, it's not possible. The only way to have images (or any form of remote resource) in emails, and at the same time avoid tracking, is attaching them.
Whether it's a header image or a "spy pixel", both of these things can be used to track you. Therefore the solution is to disable it entirely if you do not like being tracked.