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Of course, art is a subjective thing. Many people would look at a Jackson Pollack "splatter" artwork and determine most definitely that modern art is not art because it "doesn't look like anything." And if you spend any time in the modern art world, you will definitely see something at some time along the way occupying space in a perfectly respectable art museum that, to you, could never be considered art.
So is it just a matter of opinion? To some extent, yes. But there is an art world and an industry behind it that depend on there being some standards upon which art is judged. One such standard is the intent of the artist. If you produce a photograph or an art work derived from a photograph that is intended to be viewed as art, then the viewer is obligated to try to see the artistic merit in it. Whether the viewer sees that merit or not may depend on the viewer's abilities, how good you are at getting your artistic message across or many other factors.
But just wanting something to be art doesn't make it art does it? As a layman in the art world, I sometimes go with the "I don't know art but I know what I like" system of evaluating pieces I see. Art, after all, has a tendency to touch us in another place that is above and beyond the image. It is an emotional place, a place of reflection and understanding. Maybe we would say it touches our "soul". For a work to be art, there should be a message, a feeling, a reason the artist made the work because he or she wanted to say something, even if how I interpret the statement is different than what the artist meant.
So that might also be an evaluation of a photograph as to its artistic merit or not. Now the primary objection to whether photography is art sometimes is that a photograph is often a realistic depiction of a moment taken with a machine and some would say that "anybody can take a picture." The implication is that the same mechanical skill it might take to paint a picture of sculpt a statue is not needed for photographic art.
It's true that the mechanical skill that the guy at Wal-Mart might need to take baby pictures may be the same as a great photographic artist might need. But the objection doesn't hold up because the same human language is used to create great poetry as it takes yell out obscenities at a baseball game. So it isn't the skill that makes it art.
Good evidence comes from the credit some great art experts have given to photographic exhibitions in the fine museums in the world. The very fact that photography is considered art by those who know may be evidence enough. So the conclusion must be that because the arguments against the artistic value of photographs are weak and people who know consider photography to be art, then we are safe in viewing what we do artistically too. And that opens up that side of your soul to express yourself through the medium you love the most photography.