I would normally use Acad, but the photos are a little easier to read and therefore, more difficult for the contractor to argue with.
The photos are all scaled and everything...obviously, this isn't my area of expertise, but to test it, I measured a few things on the photo and then checked out in the field. I'm only measuring little pockets of the entire site...anywhere from 1/2 acre to 3 1/2 acres. It might be off a little bit, but that's alright. It doesn't need to be right on anyway. Apparently, we got charged waaaay more than we should have last year for weed control. These measurements will be going in the PO and given to the sprayers so they don't try to pull another fast one. Those of you who do this sort of thing everyday would likely do it differently, but this seems to be working pretty well for now.
Thanks guys!