Flickr is a great photosharing website! It is great that you have the ability to use some pictures from Flickr's creative commons for free! I love the way you can join groups (where you share commonalities with others, and can share pics or info based on these commonalities). I also love that you can map where pictures were taken! This is a great tool if you are wanting to show your class something and need to give them some perspective on where it happened. I also learned that a Tag is when you identify a picture to fit in a certain group.
Librarians use Flickr to share ideas, have author and book discussions, and disperse information to other libraries(including public libraries) about their program. Here is a picture that I found. I was thinking of using it in a lesson about a hero we study, Jane Addams.