IIRC the manifest doesn't require the files to be in order either, just listed...
In any case, the procedure I gave you will reorder the list of images. You say that they are already numbered but not in order as they appear in the book....that doesn't make sense unless you have something before the number in the filename, OR, you don't have them numbered in the proper order. The files will be listed using the 0-9A-Za-z order I mentioned. Could you give us an example of the filenames you see?
I recommend ordering them thusly (for no reason other than it seems like it will make you feel better
):
cover.jpg
img_01.jpg
img_02.jpg
img_03.jpg