Been thinking about this for a while. I have a fairly sizeable amount of wallpapers I like to randomize, but I have most of them set under specific categories, which are all held in different folders. For the wallpaper profiles I then choose the applicable folder, or indeed folders (if I want to randomize using images from several categories). The thing is though that many of them fit under several of my categories, so I need to make copies of them all over the place, and managing them becomes a lot more difficult, especially if I also want to exclude a subset.

So if for example I had a category called "automobiles" and a category called "art", and I had an image of an oil painting of an automobile, I'd need to have two copies of it, one in each folder. And for the sake of argument let's put in another category called "gaming", and I have a wallpaper made from a screenshot from a car simulator, so I again need to copy that in two folders. Still works fairly well if I want to just randomize all my wallpapers featuring cars in them, though taking up a lot of unnecessary space. Then let's say I want to make a profile that randomizes wallpapers consisting of photographs of real cars. Now I need to be able to exclude the gaming and art ones from the pictures of real cars, meaning I have to make another set of subfolders inside the "automobiles" folder. You can see how this can very easily get completely out of hand.

So why not use a functionality that's already in Windows: File tags. When making a profile you'd select folders where to look for the images and then limit the ones shown with the tags ("include images with tag a, exclude images with tags b or c"). That way you could easily tag your files with as many tags as needed, which is a very simple procedure, could more effectively set your profiles (I personally change them a lot depending on my mood), and could avoid the needless duplicating of files and overly complex folder structures.

Sounds like a decent enough idea to me, at least.