There's a new MediaWiki extension that's just been published: MediaLoader. It looks like it's supposed to load media items such as images, videos, etc. on demand. I haven't been able to get it to actually work (there's some strange Composer loading stuff going on in its code) but I think it works by displaying a click-able bit of text such as 'Load example.jpg' (not actually a link) that, when clicked, turns into the image or whatever. All it's doing for me right now is turning into the raw wikitext, but maybe there's something I'm missing.
I guess the idea is to not download/display the image if its not wanted by the user?
Anyway, it's new, and it's always nice to see a new extension being made. Huzza!