From Syria, to Sri Lanka, to Russia, there are journalists ready to put themselves in harm's way to shine a light on some of the darkest corners of conflict, crime and corruption. What makes them do it? And what difference do they make? Stephen Sackur speaks to British photo journalist Paul Conroy who was wounded in the Syrian army's bombardment of the city of Homs last February which killed his Sunday Times colleague Marie Colvin. When, if ever, is telling the story worth risking your life?