Scanned Book- Software for creating manual index?

[leezer3]

Apologies if this is sounds a little confused, but please bear with me

I'm looking to digitise a load of old 'books'-
Book isn't quite the right term, as they're a series of hand-drawn / annotated diagrams, with some typewriter written accompanying text.
These were then photocopied in the mid-70s and comb-bound.

Obviously, with this sort of stuff, I'm never going to get OCR working, and that's neither here or there; PDF or something similar is just fine.

Where I'm a little stuck is that I want to create a searchable index for this scanned stuff. Whilst I'm going to need to enter the appropriate references by hand as I go along, I'm sure there must be a way to do this!

Most of the digitisation resources I've found are related to books that are linear in nature, not one where you want a specific diagram off a page and hence want to search the index

Anyone with experience?