Is there a photography capital of the world?

Probably not. Photography is so important to modern communications media that it is of importance everywhere. If you were to try to name a capital of any sort, Rochester, NY might be high on the list as home of Eastman Kodak, which has been over the long term the most influential organization in the world in the development of photographic technologies. But trying to pin down any one "capital" would be a hazardous enterprise.