Covers, calibre and the devices
OK, I made a statement about how the Kobo devices get the cover images. What I said was correct, but didn't take some other things into account.
So, the simplest case is that an epub is put onto the device. The epub is added to the library and when needed, cover images are generated from the first page of the epub.
If you then edit the epub and change that first page and put in on the device again, the cover image won't be updated. The new version of the epub will be the one you read, but if the cover images have already been generated, they won't get changed.
What the above means is that if you change the cover on the book, you have to delete it from the devices library before putting the book on the device if you want the cover images to change.
Now, for the rest of this, I am going to assume the first page of the epub is simply displays an image. Inside the epub is an image and the appropriate code to display it as the first page.
Now, when sending a book to a device from calibre, it updates the metadata to whatever is in the calibre library, but it doesn't change the cover image. So, when you look at the book in the devices library, the cover is still the first page of the epub.
You can fix this via a conversion or using the Modify ePub addon. Both can put the current calibre cover image into the epub and make sure it gets displayed as the first page.
The Kobo Touch driver in calibre has three cover related options. The black-and-white option is simply so that the file sizes of the cover images will be smaller. The other two, "Upload covers for books" and "Always upload cover" are about when to put covers on the device. "Upload covers for books" will copy the covers over if the book is already on the device. This is useful in the case where you resend the book to the device after it has generated the cover images. It replaces the generated cover images with whatever calibre has in its metadata. If "Always upload cover" is checked, the driver will put the covers on the device when it sends the book over the first time.
The above is for epubs in the main memory of the device. Other books types should be the same, but I haven't done as much testing with them.
For books on SD cards, the situation is different with FW 2.1.4 and later. With the earlier firmware, the device generated the cover images and stored them in the main memory. From 2.1.4, it doesn't do this. The cover images are not saved anywhere. They are generated when needed and then discarded.
That should cover everything, but if anyone sees something I've missed or want clarified, I'm happy to rave on some more.
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