Wallpaper, also called desktop background, is the customized picture used to decorate the desktop. It can be an image file with a different size and resolution than the screen's resolution and is used to make the computer desktop more fascinating and attractive.
Please refer to Deepin_Desktop_Environment - Set Wallpaper.
/usr/share/backgrounds(Default system directory for wallpapers)
/usr/share/personalization/themes/Deepin/wallpapers(Special directory of wallpapers for deepin desktop)