I understand your frustration, but hopefully you also understand the need to protect artists work. Unfortunately, in this day in age, it is really easy for people to steal work and mark it as their own. I've had someone market this before as their own and sell items with the design on Ebay. Not a fun experience.
But, I am really happy to know you liked it enough to want to use it as your desktop. And I hope this doesn't come off as snarky or rude. I just wanted to help explain why it is there. If I didn't have to worry about something like that, I'd have no problem sharing it with you.