Ubuntu comes with a bunch of default wallpapers some really good and some just okay. You may choose to display just one background picture all the time or you can opt for a slideshow of all the wallpapers that ships with Ubuntu. While you can download any wallpaper from internet or use an existing picture on your hard drive as the desktop background, you may not be able to create a slideshow of your selected wallpapers in the same manner as of default wallpapers slideshow.
Why do the new pictures not added to default slideshow:
If you think that by going to System Settings-> Appearance and adding a new picture to “Wallpaper” will include the newly added picture in the slideshow, you are WRONG! It does not happen.
Why, you ask? Because these default wallpapers are located in /usr/share/backgrounds and there is precise.xml file responsible for creating the slide show in the /usr/share/backgrounds/contest/ location. If you want to take the pain, you can edit this xml file to add your new pictures or wallpapers to the slideshow. But why take the difficult path if we can use an application for easily creating the wallpaper slide show.
Create wallpaper slideshow with Wallch in Ubuntu 12.04:
Wallch is an application that gives you full control over your wallpapers. You can create a slideshow with your chosen pictures from any location. Open the terminal and use the following command to install Wallch:
sudo apt-get install wallch
Once installed, launch Wallch. You can create a directory in some place (Pictures is more suited for this purpose) to keep the wallpapers of your choice. If you are looking for some stunning wallpapers, check Elementary Os Luna’s wallpapers.
In Wallch, you can choose the directory(ies) where you have kept the wallpapers. You can set the time interval.
You should also configure the Start Up options from Preferences to enable auto-change of wallpapers at start time.
I hope it helps you to create a slide show of your favorite wallpapers. Cheers