Quote:
Originally Posted by alansplace
If you're talking about a .mobi then it'll get put in the .mobi when you add the .mobi to your kindle using calibre. The epubs will do that too, when you put it on the nook, but can also be installed into the epub with the calibre feature, polish.

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If we're talking about a MOBI it won't get the cover, period. MOBI doesn't recognize cover metadata, and must be updated by performing a full MOBI-to-MOBI conversion (or reconverting from the updated EPUB that spawned it, if available).
For this reason, amongst others, you should go with the AZW3 format, which is an update to MOBI and is a different but equivalent format to EPUB.
Since this is Harry Potter we are talking about, you should've gotten the EPUB from Pottermore, and that's what you should be working with. Make sure you are using AZW3 on your Kindles.