sudo apt-get install ubuntu-wallpapers-karmic ubuntu-wallpapers-lucid ubuntu-wallpapers-maverick ubuntu-wallpapers-natty ubuntu-wallpapers-oneiric ubuntu-wallpapers-precise ubuntu-wallpapers-quantal ubuntu-wallpapers-raring ubuntu-wallpapers-saucy ubuntu-wallpapers-trusty
If you get ERRORS as below just remove those download commands of the wallpapers giving the error from the above command. In my case it was quantal, raring and trust and try again.
E: Unable to locate package ubuntu-wallpapers-quantal E: Unable to locate package ubuntu-wallpapers-raring E: Unable to locate package ubuntu-wallpapers-trusty
Here's how you can download the wallpapers from Ubuntu 14.04 Trusty Tahr.
1. Open a terminal window.
2. Type in the following commands then hit Enter after each:
You might get an error as below related to 'Secure Certificate.'
ERROR: cannot verify launchpad.net's certificate, issued by `/C=US/ST=Arizona/L=Scottsdale/O=GoDaddy.com, Inc./OU=http://certs.godaddy.com/repository//CN=Go Daddy Secure Certificate Authority - G2': Unable to locally verify the issuer's authority. To connect to launchpad.net insecurely, use `--no-check-certificate'.
If so COPY/PASTE the command below and hit Enter:
wget https://launchpad.net/~atareao/+archive/atareao/+files/trusty-tahr-wallpaper-contest_0.0.1-0extras14.04.0_all.deb --no-check-certificate
Again COPY/PASTE the command below and hit Enter:
sudo dpkg -i trusty-tahr-wallpaper-contest_0.0.1-0extras14.04.0_all.deb
All the wallpapers are under /usr/share/backgrounds/ and they should show up automatically under System Settings & Appearance)