Configuring the GL Slideshow screensaver

This will show you how to enable the GL slideshow screensaver

To enable it go to:
System–>Preferences–>Screensaver–>GLSlideshow

Configure GLSlideshow

To change the path to the pictures edit ~/.xscreensaver

cd ~
echo "imageDirectory:	/path/to/pictures" >> .xscreensaver
echo "chooseRandomImages:   True" >> .xscreensaver

You can edit the options by changing the runtime arguments

sudo vi /usr/share/applications/screensavers/glslideshow.desktop
...
# Exec=glslideshow -root
#Exec=glslideshow -root -duration 16 -pan 6 -fade 6 -zoom 60
Exec=/usr/lib/xscreensaver/glslideshow -root -duration 10 -pan 10 -fade 2 -zoom 75 -fps
...

References

Ubuntu Wiki