Magnum agency photographers are one of the biggest groups in the world. The people that are signed up to this agency are the best of the best, I have in the past entered a competition with the agency that would have given me paid work experience if I had won the competition, unfortunately I did not win the competition as the standards were very high.
Magnum photographers make sure that they are in the right place at the right time and they try and not think about the moment just take the picture. In the video abut Bresson’s work it was said that if you think about the image it won’t work, so the best thing to do is not to think too had about what you are trying to achieve.
Also in the video it was said that you have to steal the moment to then give back. What I think this is saying is you steal the moment by photographing hard subjects, for example a child screaming in the hope that you then give back by making people aware the event, for example war is happening and what the effects it has on the screaming children in a bid to then hopefully help stop the war.
In one way a picture could be decisive because the photographer has to think about what settings and what to take pictures of, for example if a photographer was stood on a battle field and to the left was a damaged building and to the right were wounded locals the photographer would decide to take pictures of the wounded in the hope that it has a more thought provoking image, so in that sense it is rather decisive.
However if the photographer was just happening to be walking down the road and saw this out of nowhere then this could be happening independently from the viewer, but it is then the photographer who decides what angle or story he/she wants to tell in the image.