A simple script to change the background.
Just a simple bash script for changing the position of your wallpaper, and it works on Fedora 18;)
#!/bin/bash
OPTIONS="Centered Scaled Spanned Zoom Stretched Wallpaper Quit"
select opt in $OPTIONS; do
if [ "$opt" = "Centered" ]; then
gsettings set org.gnome.desktop.background picture-options "centered"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Scaled" ]; then
gsettings set org.gnome.desktop.background picture-options "scaled"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Spanned" ]; then
gsettings set org.gnome.desktop.background picture-options "spanned"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Zoom" ]; then
gsettings set org.gnome.desktop.background picture-options "zoom"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Stretched" ]; then
gsettings set org.gnome.desktop.background picture-options "stretched"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Wallpaper" ]; then
gsettings set org.gnome.desktop.background picture-options "wallpaper"
echo You choose the background-picture to be $opt ! | tr '[A-Z]' '[a-z]'
elif [ "$opt" = "Quit" ]; then
echo done
exit
else
clear
echo Bad option
fi
done
source: https://ask.fedoraproject.org/en/question/24825/on-gnome3-how-can-i-center-an-image-as-my-wallpaper-or-maybe-stretch-or-tile-it/