I'd imagine that they are going to de-dup the images they proxy which means email marketers need to generate unique images per mail and that means no more 1-pix

I'd imagine that they are going to de-dup the images they proxy which means email marketers need to generate unique images per mail and that means no more 1-pixel tracking images. A solution would be 1-pixel high tracking lines - a 1 x 128 pixel wide image that encoded 0 and 1 as two RGB colors adjacent to the mail's background color in the visual spectrum so the difference isn't noticeable would encode a sha-1 hash placed in the url. http://example.com/tracking-line/{hash}.png