Wow, I think everyone is getting a bit carried away here. I totally agree with enforcing copyright, but there are probably tons of screenshots and preview images using other peoples wallpapers here on WC. Some state who the artist is, others do not. Some are even original to the OS and owned by Microsoft.
I see how this screenshot though can easily be edited to create a full-sized wallpaper image, but so what? If it can be downloaded elsewhere legally on the Internet, why would someone waste their time editing a screenshot anyway? I know if someone were to use one of my walls (albeit not very good
), I would feel honored to have someone show it in a screenshot. It would be nice if they gave me credit, but no big deal.
In my opinion, and unless stated otherwise by the original author or if it is being used for profit, if an author puts his work on the Internet they are intending for it to be used and shown by people, so if it is in a screenshot, they should be happy that their work is getting exposure.
Added: Oh, and with Adobe CS5 in the works with its capabilities, I guess all screenshots will have to use a blank background then unless it is your own image too right? 