instant calibration from photo of a map

what happens quite often on a long tour: you could not get proper maps of a specific area in advance but when you get there, you find something really nice in a book store or on a sign at a trailhead. what to do with the silly analog data? it would be great if i could simply snap a picture and do a quick and dirty instant calibration/conversion to oruxmaps. of course it wont be highly accurate, but still way better than no proper map at all.

instant calibration could work like this: oruxmaps offers "import graphics file". it places the picture half transparent on top of the current map (north up mode, covering about 80% of screen as a start). left/top and bottom/right edge are draggable points. i could then drag those edges around until the new and better map more or less matches whatever i can see below.