Whilst looking through YouTube videos I came across this. A genius and really funny idea called the 'Fulgurator' it allows you to manipulate a landscape by projecting an image or text as soon as the built in flash sensor is triggered from another camera. This means the image or piece of texts is only visible in the photograph taken, leaving surrounding members of the public very confused when they see something in their photograph that isn't there in real life.
This is what it looks like.
Julius von Bismarck and Santiago Sierra go to certain famous places all over the world where there will be lots of tourists taking photographs to use the Fulgurator. For example Julius used it to project a cross on to Barack Obama during an important speech. its funny to watch the public around him looking in disbelief at their cameras. My favourite is when they projected NO above the Pope at World Youth Day in Madrid. I'm not quite sure how they get away with it as I'm sure both the Pope and police wouldn't be too happy to see NO written in large in every photo taken with a flash that night. Take a look.