People who claim photography isn't art, or is a lesser art, are generally (I find) doing a poor job of separating the conceptual side of art from the execution of art.
Executing a photograph is easy. Despite claims to the contrary, there isn't really a "making" step necessary to call into being a photograph. Yes, you can do all the work you like on it afterwards, or beforehand, but that's not the part that makes it a photograph.
Executing a painting or sculpture or a novel is considerably more demanding, you actually do "make" something, with a long and involved series of mechanical steps, each with your brain pretty well engaged, over a period of time.
But that doesn't mean the conceptual part isn't just as difficult and just as valuable. I have argued in the past that photography is essentially an act of "selection" and not of "creation" as such, but that selection should be treated as an equal to creation.
The justification for that equality could come from several places, I dare say, but at any rate you can remark that a photograph can produce results in the viewer just as well as a painting does.