Creepy Google

Maybe you accidentally set the image as your desktop background. Or if not, maybe someone else did.

Yeah that's probably right you could have been surfing and set it up as background by mistake before you logged out and didnt notice it =/, at least someone else have access to your account aswell as upon4 said.

as creepy as its seems its unlikely anyone else
did this unless you have a ssh server with a weak password

the chances you or someone else did it by mistake

if it is the case that google are remotely changing everyone’s desktop background(i rely dont think they are)
they would use a higher resolution image!

Do you use any 3rd party repositories? Those can do anything to your machine.

You could try clearing your browser's cache to see if you set a cached image as a background.

that would creep me out!