What site does it work on?
oh, when I save it to my drive it works
it depends on how the browser renders jpgs iirc
well, we don't thumbnail as .jpg here, but it looks as if it's a combination of the browser and the thumbnailing algorithm these specifically target.
Because the image looks different on download, on 4chan and on kissuhttps://puu.sh/I8LFa/56dd41daf6.png
Perhaps it's the -thumbnail %dx%d that causes it to no longer become an alternate image, but I'm not willing to test this much more
what else is quite interesting is that if I resave it from >>77408
it loses the ability to have multiple images.