A whole bunch of 1950's style dime novel covers re-imagined with a public library theme. While most are not school friendly, they will prompt a laugh from anyone who has worked in a library: public or school.
"SYNC is a program that gives away two complete audiobook downloads–a current Young Adult title paired thematically with a Classic or Required Summer Reading title–each week to listeners ages 13+ while SYNC is in session each summer."
SYNC gives away 2 FREE audiobook downloads every week each summer. In 2014, 26 titles will be given away over 13 weeks starting May 15th.
Think about what desktop wallpaper you use. Is it the default, or has it been chosen to reflect your library's atmosphere or policies? You can select a "book themed" image, or even superimpose a reminder about computer behaviour on an appropriate scene.
Haiku Deck can help you create attractive images with a message.