Apart from displaying images from local folders, several different online sources can be used to fetch wallpapers according to user-specified criteria.
Variety can also automatically apply various fancy filters to the displayed images -- charcoal painting, oil painting, heavy blurring, etc. -- so that your desktop is always fresh and unique. Applying a heavy blurring filter for example is a great way to get abstract-looking and unobtrusive, yet colorful wallpapers, similar in spirit to the default one in Ubuntu.
Install Variety wallpaper changer in ubuntu 13.10
Open the terminal and run the following commands
sudo add-apt-repository ppa:peterlevi/ppa
sudo apt-get update
sudo apt-get install variety