1 You need, in your $PATH:
3 - ocropus (this drags along a horrible set of dependencies, sorry. A future project is extracting the tiny part scandal actually uses.)
4 - ImageMagick (in particular, the convert utility)
5 - pdf2dsc, part of ghostscript (which you'll also need to allow imagemagick to process pdfs)
6 - a standard saneish linux/bsd environment (both Linux and OS X work)
7 - (probably) bash - I haven't made or checked its compatible yet.