It took me until now to figure this out. It seems that when using the background chooser included in JWM-desk, if the image is changed to fit the desktop, I believe using the "distort" option, then a backup image is created in a directory named after the source directory of the background and pre-pended with "Original" -- as in an image that came from /mnt/home/geobackgrounds that has been distorted to fit the monitor resolution will be saved in the source location under the original name, and the original file moved to /mnt/home/Original-geobackgrounds.
Since I collect backgrounds and load them from my collection directory, I don't like that it moves the original because it's confusing. Any one else notice this? I've been using this utility for a few years but it just now became clear what was happening. I initially thought that gimp was creating the backup directory when I edited an image, but I believe it's the background changer now.