The funny thing is that when I saw Roger Ballen lecture last summer, he gave off a sort of imprisoned energy. He paced the floor like a caged wildcat. His speech was sharp yet meandering, a bit like a prisoner of conscience shouting through bars. You know in your heart of hearts I'm right mixed with Can anyone hear me? I think some of that feeling is in his photos.
Brook's Prisonphotography blog is good reading from an under-represented point of view, and potentially practical too. Considering the trend in anti-photography legislation there's a chance any shooter can land in the pen. Just pray you don't wind up in the Shadow Chamber.