We had a visiting artist at the school I worked at for the past five years. He showed up the first day and has not left. He got his teaching certificate because he had no idea how much he loved teaching. He takes time off every so often to set up a public sculpture, or finish and deliver a painting. Teaching is his hobby and does not pay his bills. His impact on the students will probably not be noticed by them for a few years but what he does in the classroom is amazing.
I would want a real hands on alt photographer. Someone with a range of abilities and the ability to communicate. I also don't want someone who is "famous". Kerik springs to mind. Or Sandy King, but his expertise might shoot right over our seventh graders' heads. Hell, personal hygene shoots over many a seventh grader's head.