Not all photographs are art, in the same way as not all sketches or drawings & paintings are art.

To be "fine art" a photograph or often a series of photographs is generlally of a standard that would be acceptable to a range of galleries and publications, and sold to collectors.

The term isn't specifically about subject, technique, fame, commercial success etc but is more about how work is perceived, conceptualised, executed and presented, and the photographer needs to be able to articulate the background to the work putting it into context vwith contemporary photographic practice.