For many of those who traffic in images, producers and consumers alike, witnessing is an essential part of the project. Witness testimony is evidence, and something more than evidence. The act of witness is not confined to the laws or the scriptures, though it smacks a little of both. Witnessing shapes history and memory. All over the world, society is saturated in images and image-makers clamouring to bear witness. What do pictures want? To testify!

It is often remarked that artists bear witness. They have done so since the beginning of time. It is less often remarked that works of art themselves bear witness. The most celebrated example in recent memory may be Picasso's Guernica (1937), reproductions of which were worn as a badge of honour by anti-war protestors on the eve of the Iraq War in 2003: warning and witnessing at the same time. Another example is Klee's Angelus Novus (1920) – Walter Benjamin's ‘angel of history’ – a survivor who bears witness to the terrible twentieth century (see Chapter 3). Ironically, when it comes to witnessing, the testimony of the author of the act is not always to be trusted. Artists (and other makers of graven images) are rarely explicit or programmatic; often they obfuscate their purpose. Occasionally, someone makes a statement. The mottos of Goya's Disasters of War (1810–20) are legendary: ‘One cannot look at this.’ ‘I saw it.’ ‘This is the truth.’ In the Western canon, or the Western way of witness, Goya is the gold standard.