Any object (in this case photos) that may elicit an aesthetic response is potentially art. But only these objects which have been cherry-picked and promoted for aesthetic consideration, primarily by museums (but also galleries and similar venues), are actually art. So, calling something 'art' is a convention, not too dissimilar to the public act of christening. (There are differences: you cannot be unchristened but a work that once was declared 'art' may fall from grace or be forgotten.) This is what one does when they baptize their work 'art' or call themselves 'artists'. But one does so prospectively without really having the discretionary power of an institution like a museum to inaugurate something as art. Of course critics and museums also deliver judgements that are subjective, but the consensus of the 'art world', whatever that is, is an established fact. The main problem is to negotiate some kind of balance between the private, visceral experience we all get when confronted with art, and its public assessment and ensuing canonization as such.
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