When I scan a lot of old photos, to catalogue my family albums, I need to do fast due their number. I simply put them on a A4 paper, with a bit of glue, then I scan all, creating an image composed from 5-12 small photos. To divide them, I use this script, that call Imagemagick convert, that divides in more images.
Script is really simpler, not professional, but works for me.
Photodiv script is on my repository on GitHub.