Picture of drug-addled Ukrainian prostitute among the most startling press photographs of 2012

From the disturbing image of a drugs-addicted prostitute smoking a cigarette, to a haunting picture of a desperate mother standing alone amidst the devastation of the Japanese Tsunami - the World Press Photo contest offers a vivid reflection of the world we live in. An exhibition of the winning entries, which went on show at the Southbank Centre in London today showcases the best in photojournalism from across the globe and features startling pictures from the world in 2011.