Otago Central Railway [47A]: Cromwell Gorge Maps revisited?

I suppose when you look at the maps I have done, while they are interesting, they would be even more interesting if the historical aerial photography was overlaid into the present day aerial photography. This is really easy to do at a base level with Google Earth, but not so easy with the other tools I have at my disposal. Obviously I can’t use Google Earth because of their licensing terms.
It is something I will take a look at if I have time, but it is going to need me to become really proficient with Gimp or Paint.net to (essentially) splice the old imagery over the present Linz aerials, and then do the maps again over the new imagery, which has the advantage of already being georeferenced. 
Meanwhile it’s time to draw the next station layout, which is Lauder, and then carry on down to Ranfurly. Hopefully there will be more aerial photos available by then.

UPDATE: After playing with Gimp and Paint.net, Gimp turned out to be simpler than I expected once you get the hang of the various capabilities. The initial part of getting the images lined up isn’t as hard as I expected, being really much the same as doing it in GE, you don’t need to know about alpha channels and masks and things to get to that stage. Paint.net isn’t quite as easy to use at this level in my opinion, or maybe the loss of functionality is the issue. After trying both I have settled on Gimp for now, although admittedly having it on MainPC is easier than working on the Windows 10 computer with its smaller screens that aren’t straight in front of me.

Of course once the hard part of lining up the images is done then a bit more learning would bring me the capability to paste in the old riverbed into the current aerial imagery and then be able to draw the maps over it more fully. I expect all that is needed for this is to be able to turn the current relatively smooth riverbed into a selection and then merge the old aerial layer into it. I am sure there is a name for this in Gimp/Photoshop jargon and eventually I will learn this.

However having the time to do this is crucial and it’s probably going to have to wait as I have plenty to keep me busy for the present.