Download all the Ubuntu Community Wallpapers from Karmic Koala (9.10) to Trusty Tahr (14.04)

Open your terminal (CTRL+ALT+T) and COPY/PASTE the commands below:

 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:

 wget https://launchpad.net/~atareao/+archive/atareao/+files/trusty-tahr-wallpaper-contest_0.0.1-0extras14.04.0_all.deb  

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)