Shotwel is a popular open-source photo management tool. Yes, you can also manage your wallpapers automatically from this tool. You might already have it installed in your Linux PC, but if you don’t, you can install it with the command below or download it from the Software Center/Package Manager:
sudo apt install shotwell
Variety is a light, powerful and open-source program for changing the wallpaper for Ubuntu Linux. It can also fetch images from Unsplash, Bing, and Flickr.