Libraries provide amazing programs for the community. Why not share these programs with a larger audience using the Raspberry Pi to stream video? I guarantee your marketing department will be excited to try this and you can broadcast your event to using social media networks.
Ustream put a tutorial up and your IT Department or local user group can help you get it setup.
Streaming video has other applications. Do you need extra security? How about a program to help library users make a bird cam?
What other applications do you see for streaming video? I thought we could put a live camera for kids to check on our turtle Munch.