Is the author not aware that for the last decade or so every email program/service in the world prompts the user to load images to purposely thwart image tracking?
While that is true, people say "yes" because things don't display properly. Often elements like emoticons and whatnot are also remote images!
"Display remote images? Yes/No" is an all or nothing proposition, in other words.
The e-mail client, rather, should determine which images will display in a visible way and reject all others even if the users says Yes. It should not fetch images whose tags don't specify a width or height, or that specify one less than 16x16 pixels, and those that are positioned such that they will be clipped, or clipped by something else, so that even if filled with fetched content, they will not be visible. Basically: calculate the set of image tags that refer to images which will be obviously visible to the user. Prompt for those, and do not fetch the rest regardless of the answer.
Of course, the standard user has no idea what that means, how to judge where the email comes from, or what any of the options mean beyond "see the pretty pictures", but, hey, one step at a time.