(Yeah, the width/height provided in the HTML for an image acts as the default for the associated CSS property; basically, it acts like it's part of the CSS, but at the lowest possible priority, so any other CSS wins.)

Thank you, that's helpful. It's looking like tables are still fairly popular for this sort of thing, and it's real unlikely to have a "casual" image in one, so that's one strong candidate for squash exclusion.

I think I'm gonna have to creep around in comms where people share codes and hunt for commonalities in non-table markup. I KNOW there's got to be a bunch of y'all using nothing but divs, and I really want to find some way to distinguish that markup from casual images that roll in on random feeds and on copypasta embeds from image hosts.