As I mentioned in the article about tablets changing the eBook marketplace, Apple is upping its cover image requirements – to 1400 pixels across on the shortest side. You can even see this using iTunes Producer:
Okay, so not a big deal, right? Just enlarge all your images…
So, it has to be 1400 pixels…but not more than two million pixels total…[bites tongue, does math in head]
So to satisfy both these requirements, your cover image (in the ePub) should be 1400 pixels by 1428 pixels.
I’m hoping someone at iTunes will see this and get it resolved.