Somewhere there is a tutorial for doing it, but I couldn't find it tonight when I posted those links. I'll keep looking.
It's a matter of lining up the laptop and then closing the lid and snapping a picture - so you get the stuff behind it, and then cropping that image to use as wallpaper on the screen.
It wouldn't be that hard for a straight head-on picture, but some of them are done at an angle and that would take some doing to get it just right.
I'm just guessing, the more I know about cameras and image manipulation, the worse my pictures turn out
Take care, Margaret