on the "preferences" - "look & feel" you can choose only one picture for your plex backgound. i good new feature would be that you can choose a directory which includes some pics and set a rotation time (with a sort by name, date...) and a random time.
very useful because it could increase the motivation to work with your brain and so the time of use of the brain.
if you are choosing fotos from your last holiday or erotic photos the brain starts to live. with the positive emotions you got work with the brain brings more fun.