Allow more image sizes for fan art
The image size restrictions are pretty severe in my opinion. Besides 1280x720 and 1920x1080 resolutions like 1920x1200 and 2560x1440 could be considered. Perhaps even 3840x2160, with the rise of UHD. Since those last two resolution are 16:9 ones, they should scale fine to any screen with a resolution of 1920x1080.
I included 1920x1200 in my list as well since it’s a pretty common wallpaper resolution. In my experience wallpapers of that size can be easily scaled or cropped to 1920x1080 without the image being warped too much.