Following on from bug #740588, the wallpapers in Ubuntu come from the Ubuntu Wallpaper contest:
There are ~30 shortlisted entries and a selection of those have been chosen. There are two types of image, most are photographic (JPGs) with a small number of non photographic images (PNGs).
1. Publish the list of winning entries on design.canonical.com
2. All images are CC-BY-SA which is a criteria for inclusion and this was a stated requirement of submission. Contributors have been asked to update the relevant metadata on Flickr
3. Scale all the images to the same 2000px width and corresponding height to maintain aspect ratio. If in doubt this should be done from the centre.
4. I understand that compression is managed when it's packaged so if it's oversize we can recompress/ reduce the number of images. For reference our current wallpapers are around 4MB and we anticipate this will be about the same size.
5. Upload to main
Note that it is not possible to directly download the images from the shortlist group because not all members have Flickr Pro accounts. Iain will source all the images we need direction from the artists and will attach them here. Sladen will spend an evening tweaking compression settings so that all the images still look good.
The format of the filenames references the artist and I have named the file using the existing convention of Image_name_by_Artist_Name.jpg/.png