Pictoric is a simple tool allows you easily creating a desktop slideshow in Ubuntu. It works on Unity desktop by default, will work on gnome by a little configure on .desktop file.

Install Pictoric on Ubuntu:

First download .deb package of Pictoric from:

Download Pictoric_x.x_all.deb

Then double click to install it, or using this command in terminal:

sudo dpkg -i ~/Downloads/pictoric_*.deb

Use Pictoric to create a desktop slideshow:

Launch Pictoric from the dash home, or from System Settings window:

Then select a folder on Pictoric window (on drop-down box choose other), input a time interval, finally click apply.

Make Pictoric works on Gnome:

Edit /usr/share/applications/extras-pictoric.desktop with this command in terminal(Ctrl+Alt+T):

sudo gedit /usr/share/applications/extras-pictoric.desktop

Add # before line OnlyShowIn=Unity;

[Desktop Entry]
Name=Pictoric
Comment=Setup Wallpaper Slideshow
Categories=Utility;Settings;X-GNOME-Settings-Panel;X-GNOME-PersonalSettings;
Exec=/opt/extras.ubuntu.com/pictoric/bin/pictoric
Icon=/opt/extras.ubuntu.com/pictoric/share/pictoric/media/pictoric.svg
Terminal=false
Type=Application
#OnlyShowIn=Unity;
X-GNOME-Settings-Panel=pictoric

Enjoy!