This is a slightly touched up version of White Orchid.
This photo is licensed under a Creative Commons Attribution Share Alike license (Norwegian). Please feel free to use it in your Free cultural works. I will be very happy if you let me know of your use (and I will place a link to it here), but you need not ask my permission, as long as you adhere to the license.
UPDATE: I'm very happy to say that this picture has been used in Sophie Addisons fundraising book White as a colour! All proceeds from the sale of this book will go to the MS Society of Canada.
UPDATE 3: Ubuntu 10.04 is being released on April 29 2010. For this release 16 other photos has been chosen to be included. I was lucky enough to be asked to help pick photos for the shortlist, and two of the ones I picked was used.
If you really like this photo and/or some of the others chosen for inclusion in Ubuntu 9.10, you can get them all in 10.04 and later with just a few clicks. Open Synaptic and search for "ubuntu-wallpapers-extra".