Sentence:  When I arrived at the lab this morning he was back sitting in front of his computer, a million miles away, leaning forward on his elbows and staring into the depths of space. He has changed his <WSD>screensaver</WSD> again. The Orion nebula has been replaced with some other astronomical scape, far bleaker in its appearance but more realistic. It looks like the outermost edge of the universe. 
Meaning of the word marked with <WSD> tags:  The background picture of a computer, smartphone, or similar mobile device.