I've noticed that the cover image that Calibre includes by default in epub files is a large png file. Space is at a premium on my Android phone so I would like, preferably, to have no cover image in my ebooks, or if that is not possible to have a much smaller image included by default.
I'm not sure from the above discussion about the "no default" option whether a "no cover" option is available. (I can't find a menu with "no default" in Calibre.)
If, for some reason, it is not permitted to have "no cover" can I include a blank (or very simple) gif as the default, in order to reduce the file size? If so, how?