This is a selection of 90 of the most impactful photographs, that provide a map of the past 100 years, from the epic to the intimate, the heroic to the barbaric, that literally changed our world. Photographs of the Wright Brothers conquering the air; Martin Luther King making his "I have a Dream" speech in Washington; the massacre in Tiananmen Square, do more than report they have come to symbolise whole epochs and become part of the universal visual memory in a way that few works of painting have managed to do.