[Something1234]

That's what the width and height attributes on the img tag are for. They're hints. Things can be redrawn later. Although I think I've been seeing a lot fewer images on the internet lately, but they must be hidden with css.

[yoz-y]

I know. And I wish my static site generator of choice (Hugo) added the tags automatically to the HTML.

Would it be possible to download just the headers of images first to get the metadata?

[Something1234]

It's still a decent amount of overhead to even make the request for those bytes.