Arches

Below is a photo of me in 2006 at the King Fahd University in Saudi Arabia for a workshop on preparing high school students for university. The arches that recede into the background of the photo are the same size and are equally spaced at intervals of 2.5 meters. How far away is the camera from the front face of the first arch?

What I want is a geometry solution. And of course you are allowed to make measurements on the photo.