I am more than confused, now. I am dumbfounded. I have never, in over 20 years, seen any file from "My Pictures" show up as available for Desktop Wallpaper which I did not request to be available by right clicking it and asking that it be set as such. On my home computer, I have around 10,000 jpg's in "My Pictures" and sub-folders and not one of them has ever offered itself up for use as Wallpaper. It would be a big job trying to locate a specific file in that tiny little featureless dialog box that serves as the gateway to wallpaper selection, it would seem to me. Perhaps there is a file association switch that controls or allows this phenomenon; something that defines where "Background Files" are located.
Please let me know your thoughts.