Librarian Thomas Guignard (a.k.a. timtom) has a wonderful collection of Creative Commons photographs of libraries he's taken over the years.
He says:
My interest in library architecture started as I was involved in the planning for a new library building. Looking for inspiration, I started researching and then visiting other libraries that were moving into new spaces or undergoing a revitalization. I often photographed details that struck my interest, and gradually became fascinated with the unique visuals offered by all libraries, big and small. To this day, I make a point of visiting as many libraries as I can when traveling, and often plan my trips around buildings I'm interested in visiting and photographing. My libraries bucket list never stops growing. I have started collecting some of my favourite examples of library architecture here, many more can be found on my Flickr and Instagram feeds.