I’m surprised I could not find a recent related topic.
Over the years I’ve come across some spectacular photos that ended up as desktop wallpaper. One from the Santa Cruz area on a defunct forum comes to mind, but I have to track down a current link.
Right now I’ve got the CSX “First Responder” and Military locomotives as they passed over the Deshler Diamond as my wallpaper. It’s a screen capture (ALT + PrtSc). Since it’s never leaving my computer, I’m not worried about copyright issues.
There are myriad opportunities to “borrow” images - in fact, seems like I’ve seen “set as wallpaper” as an option if you right click on some images.
If you frequent the many live cams, you may catch a favorite locomotive and do a screen capture. Just remember that most such sites plainly display their copyright claim.
I’ve browsed railpictures.net and any number of other sites, both foreign and domestic, for images to use as my wallpaper, which I usually change weekly.
It was a shame when fotopic.net folded, they had a lot of good collections of foreign railroading pictures.