Only 19 wallpapers were included into Ubuntu Karmic Koala in a competition where lots of wonderful wallpapers were submitted. Kenneth Wilmer has packed those wallpapers into a package and put them in his ppa repository.
Follow these steps To get extra wallpapers for Ubuntu Karmic Koala
1. Add Wilmer’s repository by typing this command in a Terminal:
sudo add-apt-repository ppa:kwwii/ppa
2. Update this repository by running this command in the Terminal:
sudo apt-get update
3. Install the package by using this command in the Terminal
sudo apt-get install desktop-backgrounds-extra