I believe you will find it is sufficient to send the book using calibre.
There are two ways the Kindle gets covers:
- If the book is a PDOC (has that ugly "Personal" banner) it will be extracted from the ebook file.
- If the book is Just A Book, it attempts to download the cover from Amazon's servers, using the exth 113 meta field (ASIN, a/k/a Amazon product ID). Stupidly, won't even try falling back on the embedded cover.
calibre works around this problem of non-PDOC ebooks, by sideloading the cover thumbnail itself, into the
Code:
[userstore]/system/thumbnails
directory where thumbnails are kept by the Kindle.
I've never seen missing thumbnails when sideloading via calibre, but I see them all the time when sideloading via the File Browser.