The default wallpapers of the upcoming Ubuntu 13.04 (Raring Ringtail) operating system have been unofficially posted on the Launchpad website, managed by Canonical.
Looks like there are 13 wallpapers in total, and they represent the winners of the Ubuntu 13.04 wallpaper contest, which took place on Flickr.
In order of appearance, the names of the default wallpapers in the Ubuntu 13.04 are: Begonia by fatpoint21, Blue frost by ppaabblloo77, Brother typewriter by awdean1, Cacomixtle Ubunteno by Carlos and Paula Morales, Fleurs de Prunus by Jerome Boivin, La Gomera by Alfonso Aguirre Arbex, Landing by Nic Dahlquist, Last breath by Francisco Javier Epinoza Perez, Leftover by Sagar Jain, Morning Sun on Frost-Covered Leaves by Gary A Stafford, Stop the light by Mato Rachela, Trazo solitario by Julio Diliegros and Winter Fog by Daniel Vesterskov.
You can view and download them from the image gallery below. However, be aware that these are not the final versions to be included in Ubuntu 13.04, as the Ubuntu developers will modify them a little to look and fit better with the Ubuntu desktop.