XnView Software

Since this program catalogs the location that all thumbnails refer to, it shouldn't be too difficult to have a switch where the directory tree shows either the full tree or only those branches with thumbnails.
While it would be more work, I would also suggest that this function be tied in to the ...

Setting the base directory this way works if all your pictures are all on one drive. If you have them spread over many drives like me, you need go into Windows disk management and reconfigure all your drives with pictures as directories. This requires at least one drive be formatted as NTFS before ...