What does file size have to do with anything?

Edit: I forgot the grandparent mentioned them. Ublock Origin implements the parent's proposal,so I mentioned it.

Focussing on file size is a mistake because you can just make the tracking image display something decorative or whatever. I was referring to a solution for not loading third party resources without manual approval, which would need to be more general than just blocking single pixels to be robust (although hueristics might be good enough for some cases)