...
And for the sake of people stumbling across this, you can do the same on linux by installing `gnome-epub-thumbnailer`, (it actually does MOBI as well) which integrates into any gnome-derived desktop environment, e.g. gnome, unity, cinnamon, MATE...
It is most probably available in your distro repository.
Windows users can see this thread for EPUB:
https://www.mobileread.com/forums/sho...d.php?t=208260
And this for MOBI:
https://www.mobileread.com/forums/sho...d.php?t=128030
In addition to the OSX quicklook plugin for EPUB, our very own pdurrant has a MOBI/AZW3/AZW4 quicklook plugin here:
https://www.mobileread.com/forums/showthread.php?t=25603