Originally Posted by JSWolf
You do have a way of a doing it if you have an AZW3 version of the eBook. I know you have a Kindle and there is no way of doing this with a Mobipocket eBook. But with the AZW3 version, you can use Tweak eBook in Calibre to replace the generic cover with a cover image of your choice.
Cough... there used to be no easy way to do this for Mobipocket books. But now there's my Python script and AppleScript wrapper
that make replacing the cover on a Mobipocket book extremely simple on Mac and relatively simple on Windows/Linux.