The Sturgis Motorcycle Rally website contains a gallery that is full of pictures of past rallies, organized by year. There are also pictures available at sturgisrally.com, sturgis.com and the Travel Channel website.
There are a variety of Sturgis rally books on Amazon that feature photographs from multiple rallies, or particular individual rallies. Some focus on photography at the rallies, while others focus on the story of the rallies, but most of them have photos of the locations, riders and motorcycles of Sturgis events. Sturgis rally photos can also be found in magazines as part of articles on, or coverage of, the rallies. .