It scans its own folder for image files, and then shows corresponding thumbnails for those--a catalog app, in other words. Subfolders are linked automatically. I still have to safety-check the input a bit more; feel free to tell me how to do any part of it better than I did.
I couldn't find a way to include it in this post without numerous errors, so you can read it [link|http://www.semishake.org/catalog.py|here].
And, no, I'm not missing the irony that, for my first python program, I'm explicitly performing local file I/O which the designers have tried to protect me from by not supplying me with the current working directory. Meh.