This is a puzzling question. What makes a particular photograph “art”.
The technical quality of the photo? (thinking about physical (analogue) techniques vs. digital effects)
The content / context relationship?
The person taking the photo?
The context of which the photo is displayed?
A unique vantage point?
A conceptual quality?
Can the photograph (object) just be that which is simply a beautiful thing itself to view – or does the subject “in” the photo matter too much ?
That which provokes an emotional response – to me, to you and me, to a bunch of others ?
That which makes the ordinary seem extraordinary?
That which allows us to see the thing that normally is missed?
See also Michael Wesely: Open Shutter at The Museum of Modern Art
and more about Wesely here http://www.wesely.org