And, to my chagrin, I’ve been doing it wrong.
Luckily, the fix is a simple tweak to content.opf. Previously, I told you to do this:
Yeah, no. Change it to this instead:
and then when you’re declaring your images, make sure you declare it as cover-image, like so:
I’ve updated my helper script to do this automagically – if you’re on a Mac or *nix, you can use it. And if you want to see the whole content.opf, my default style.css, and (and my other eBook utilities), swing on by this GitHub repository.