How to change wallpapers Automatically in Ubuntu

Manual wallpaper changing method: -

You can right click your desktop, select "Change Desktop Background" and choose any one of the wallpapers pre-installed, but you need to do it each time you want to change a wallpaper.
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What about changing a wallpaper automatically within a certain time interval? 
Install the wallpaper changer Variety and see the magic

 

Press Ctrl-Alt-T to run Terminal.

  Enter sudo add-apt-repository ppa:peterlevi/ppa
   Enter sudo apt-get update
   Enter sudo apt-get install variety
   Enter sudo apt-get update
   Enter sudo apt-get install variety

"With this trick of wallpaper change, you can change wallpapers in a fixed time interval from the sources you set and run it with several other settings such as randomly applying filter effects, color etc."