Cant change size of wallpaper (stock or from home/pictures) 13.10 using gnome3
Solution 1:
You can adjust your gnome desktop wallpaper using dconf-editor tool.
Open it by pressing alt + f2 and enter dconf-editor . Now go to org --> gnome --> desktop --> background --> picture-options and change its value whatever you need.
Alternatively you can change it using command line.
Use gsettings set org.gnome.desktop.background picture-options "centered" to make your background centered.