The concept of Library Snapshot Day originated in New Jersey, when librarians at the State Library and the New Jersey Library Association put their heads together and dreamed up a clever way for libraries of all types in every part of the country could show off what happens in a single day.
To help spread the concept across the land during the month of April, there's a primer and some fine examples of how it's also been done in Illinois, Maine, Pennsylvania, and Wisconsin. Wisconsin's "Say Cheese" day in pictures is a particularly clever example of how it can be done at the state level.
Library Snapshot Day is an opportunity to tell the story of how many books are checked out, how many people receive help finding a job, how libraries offer homework help, and the whole range of daily services that go on in a well-supported professionally staffed library–the very reasons the American Library Association has created the @ your library public awareness campaign and the I Love Libraries advocacy website.