Since a lot of people have mentioned that it would be useful to be able to manipulate meta data and to add cover image to a prc or mobi file I wrote mobi2mobi. Here is the description of the program:
A program to manipulate MobiPocket files. Author and title can be set and a cover image (thumb nail image for Gen3) can be added.
There are two kind of prc files used for electronic books. One is a PalmDOC file which does not have a MOBI header but can contain HTML code marked up with MobiPocket specific markup and it can be read by a MobiPocket reader. For this format you cannot store meta information in the header. The other format is MobiPocket and it has a MOBI header and some additional data where you can store meta information and an extended title.
This program can change the extended title for a MobiPocket file. It can also automatically convert a PalmDOC file to a MobiPocket file and set the title.
It can also add author information to a PalmDOC file by converting it to a MobiPocket file and set the author meta information.
You can also add a prefix to a title in a MobiPocket file. This does not work for PalmDOC files.
It is possible to add an image to the file. If there are no other images in the file then the added image will be used as cover image and thumb nail image for Gen3.
Just running the program on a mobifile without any flags will print some information about the file.
Since there is no specification available for the MOBI header this program might generate books that are not entirely correct. So keep the original file...