Each student will need a flickr account. With younger kids I'd buy a flickr Pro account (about $25/year) and we'd all share the one account. They'll need this for their flickr assignments. I want to use flickr more with students; work more on thinking visual. I've seen some awesome riffs on my idea in other subject areas.

Here are a few other interesting flickr groups worth getting lost in for while ...

Tell a story in 5 frames (Visual story telling)
Great Quotes About Learning by Young Children
Math World
Flickr For Education
Info Graphics

and my all time favourite (embedded below) is Great Quotes About Learning and Change