I find wallpapers in a number of different locations but good places to check out include Imgur and /wg/. Some of the wallpapers were probably included in default wallpaper packages from various Linux distributions that I have installed over the years.
The vast majority of these wallpapers are nature and landscape photos. There are a few abstract art wallpapers mixed in.
Because I downloaded most of these from sites like Imgur and /wg/, I have no way of knowing if there is a copyright on these images. If you find an image hosted in this repository that is yours and of limited use, please let me know and I will remove it.