OK ... the real problem here is that I used to be a professional snapper, and I can't for the life of me remember the software we used for doing this. Essentially the problem is this: say I have folder containing 5 jpegs. The file names are A, B, C, D and E. When I open the folder, the thumbnails are in that order. What I want to do is drag and drop them into the order C, A, D, E, B, select those five, click on "rename" and Bob's your uncle - next time the folder's opened, there they are, numbered consecutively but in the new order that I wanted them in.
We did this all the time, but I don't now know what we used to do it ... 🙄