Basically do a print screen command and paste the copy into GIMP/Photoshop and save the image and host it off of an image hosting site (i.e. Imageshack, Photobucket, Tinypic, etc.) Just show the link and not the full image as it'll stretch the page significantly.
As for me however, I have a beautiful screen of Lightning in Final Fantasy XIII/XIII-2 on DeviantArt. The original wallpaper is 1920 x 1080 pxls.