Alexander Andjelkovic, member of the Lubuntu Artwork Team, is proud to announce the 13.04 release wallpaper contest, as said:

As 13.04 is getting closer, it’s about time that we announce the community wallpaper contest.Submissions are done through this Flickr group: http://www.flickr.com/groups/lubuntu1304contest/And you’ll find all the necessary information about the contest there as well.
Source: FULL ARTICLE at Planet Ubuntu