A staff member removes the Iranian flag from the stage during the Iran nuclear talks in Vienna, Austria July 14, 2015. [Photo/Agencies]

Carlos Barria: For more than a decade the United States and other world powers have participated in talks to reach an agreement on Iran's nuclear program. They and Iran have spent thousands of hours around a table seeking a solution to what the West sees as a threat to global stability if Iran gains the capability to make a nuclear bomb.

The last chapter was in Vienna, where I travelled with Secretary of State John Kerry. The media had virtually no access to the meetings, but could register for photo sprays of a minute or two per day. For 19 days I sat in a media tent near the hotel where the meetings were held, waiting. The biggest challenge in such tightly controlled environments is to capture a different picture every day. Not least as it was exactly the same situation each time: people sitting around a table talking. I always planned ahead for the next time to capture something new.

On July 14, foreign ministers of the Unites States, Iran, China, Russia, Britain, Germany, France and the European Union walked on stage to tell the world about a historic agreement. Hundreds of journalists from every corner of the planet gathered at the United Nations building for the group photo and press conference.

As the ceremony ended and colleagues rushed to file their images and stories, I decided to stay on. A few seconds after the country representatives left the stage, a staff member showed up to remove the countries' flags. I ran to the front of the now empty room and waited for the last two flags to be removed. The man took hold of the Iranian flag and walked past the US flag. That was what I had been waiting for: beyond the spotlight, unscripted. When I realised that I was alone, I also knew I had an important picture that no one else had. The lesson: be the first to arrive and the last to leave.