I use gThumb for organizing and viewing my photos. One feature I wish it had (version 3.8) was the ability to list un-tagged images. I recently figured out a way to do that. I search for all images, then tag them all with the tag “temporary”. Then using the find (search) dialog I search for those images that only have the tag “temporary”. The first step of tagging all images takes a while but after that it makes it easy to find “un-tagged images.” Those are the images with only a “temporary” tag.
