Originally Posted by scoobertron
Unfortunately, with recent firmwares, the cover generation is done on the fly, rather than all at once when books are added. This means that I will either need to either find a way for each publisher's ebooks to set the margins for the cover to 0, so I can adjust the margins as desired when reading and this won't affect the generation of new covers. Or find a way, again for each publisher, to hard-code the margins of each book, except the cover, so I can keep the kobo margin settings at 0 (this may be simpler, but mean's I can't change the margins when reading, which is a pain).
The Kobo Touch/Glo/Mini driver in calibre has options to generate the cover images and send them to the reader when it sends the book. The cover images are generated from the calibre metadata and are stretched so there won't be any bars down the sides. This only works for books in the main memory. Also, it only generates the images that are appropriate for the firmware version.