[GalacticHull]

The subject basically explains the problem. Certain titles, largely ebooks published over a decade ago, show a blank white image in the cover browser. I've attached a couple screen shots to demonstrate the issue.

I'm sure this is a problem with the epub itself and not calibre.

If anyone is aware of what I can do to tweak the epub itself--either by hand or using Sigil, and certainly not using Calibre's editor--rather than just adding the cover in calibre, I'd appreciate it if you'd fill me in.