I am making Debian packages containing wallpapers that I want to sell through Canonical (https://myapps.developer.ubuntu.com/dev/). Canonical does not (that I have found) list allowed licenses for wallpapers that are to be sold through Canonical. What licenses are permitted for wallpapers to be sold?
As I already point out in my comment, the documentation isn't currently going to help you.
I would go in with the assumption that you can license a wallpaper under the same terms as most software (in that you can hold copyright, or a license to redistribute it and you can give people a license for it - this is all true in most civilised parts of the world) but you should confirm directly with Canonical that they'll accept a paid wallpaper package before you do anything.
That you're asking the question suggests that you might be thinking of a non-traditional license. Perhaps if you can expand on that, you might get a better answer... But if you're thinking of a "standard" commercial software license, I think you'll be fine.