This is a very interesting subject.
Over a decade ago I was forced to confront this issue head on. I entered an assemblage of "drug store" 4X6 prints of a portrait subject done in the Cubist manner (ala David Hockney). My twist was to partially paint over the assemblage with oils. The venue was a juried photo show at a highly revered artist organization known as the Scarab Club.
http://www.scarabclub.org/
The piece was awarded "Best of Show" ... which triggered a hue and cry from every end of the photographic spectrum. The Photographers said it wasn't photography, but instead painting ... in the same manner that painters would be loath to call it "Art" because it utilized photography. Thankfully, the Judges disagreed.
The piece eventually sold, and in the words of Warhol, to a pretty "up-there" art collector.
As a long time painter, and lover of art history, and an avid photographer who was much impacted intellectually and emotionally by many master photographic works, I had to think this through myself and come to grips with it.
My conclusion wasn't easy to come by, but in the end was elegantly concise. My answer was "Intent".
In the case of my portrait piece, my intent wasn't to take a photograph, or to make a painting. It was to do a study of "Time & Space" which is the underlying concept of Cubism. The media used was part of the intent to further explore an idea. Sort of inseparable.
IMO, if one sets out to create art, and has some intent other than taking a photograph, then it can at least be considered as art ... whether it actually ends up as art probably depends on how faithful one is to the original intent. In the hands of an artist, any media can become art. Picasso wasn't only an artisan/craftsman when he worked in clay because he was exploring his artistic intent via the medium of pottery and ceramics. Same with Fernand Leger, etc.
To my mind, "art" and "artistic", are two different things. A photo can be "artistic", but not necessarily be "art". In a manner of speaking, true art is the philosophical forward guard of visual thinking. So called "High Art" explores beyond that which exists and captures new ground ... which is often why it causes such disruption of established views of art.
I view much painting as being artistic because, while it is beautiful and engaging, it often follows someone else's art. With my cubist portrait, I wanted to push past Hockney's photographic Cubist approach and see what paint would bring to light. Mostly because it was Hockney himself that said Cubism had not been full explored yet. Not earth shattering, but an incremental personal step in which I at least stayed true to my original goal. The judges saw past the media used and validated that intent.
Also, IMHO, most photography that captures our attention is artistic, but hardly can be called art. However, there is photography that transcends that ... mostly because it goes deeper by means of its original intent. There ARE those that "Invent" ... those that devise by thinking, and come to discover something new.
Among others, Cindy Sherman fits my notion of photography as Art. She was studying painting before turning to photography as being less confined. Her intent wasn't necessarily photography, it was realizing conceptual ideas for which photography was quite capable of in her hands.
This is probably to simplistic a view for such a complex subject. Amused intellectuals will scoff at it, and a lot of photographers and painters will bristle at it.
I see myself as participating in artistic photography. I react to my surroundings and derive satisfaction from recording split seconds of the human condition as it is today. No new art new there except the application of an original invention to a narrow swath of the contemporary scene ... a continuation or validation of another's invention so to speak. I may someday "stumble" on something inventive because my mind works that way. Accidents in Art do happen
I only hope I recognize it when and if it does happen.
On the other hand, I see my dear friend Irakly Shandize as moving closer and closer to being a true Artist because he is close to finding his intent and inventive discovery using photography as the tool of expressing his ideas ... some of which are pretty damned dark ... which isn't surprising coming from a product of the Soviet Union ... LOL.