If you work with students who use school Chromebooks, you will find that some of them go crazy changing their avatar and wallpaper. Sometimes they choose very inappropriate things. I'm not a huge fan of banning something, but sometimes it is a decision from leadership or the school board. Our elementary school director asked me to set the avatar to our school logo and the wallpaper to the school logo as well. Several of the teachers were tired of seeing crazy avatars and wallpaper, so this is how you can make a universal avatar or wallpaper for your Chromebooks. Sign in to your admin console. Go to Devices-->Chrome-->Settings-->User & Browser Settings. On the General tab, you will find the place to upload the image you want for avatar or wallpaper. These are user settings, so students will need to log out and log in to have the settings take hold.