I've been reading an interesting article about photography by Prof Robert Hariman here: http://www.nocaptionneeded.com/2014/02/judging-photography-awards-much-art-much/
In it, Hariman briefly draws on the work of the cultural theorist Siegfried Kracauer, who described the polar tension within photography: “there is on the one side a tendency toward realism culminating in records of nature, and on the other a formative tendency aiming at artistic creations.”
It's this tension that causes aesthetic problems for photography. It's a tension that arises from the indexicality of photographs: photographs are pictures that show the objects that were in front of the lens when the pictures were made; they are thus simultaneously both a trace or record of the patterns of light reflected from the objects in front of the lens and a picture or representation of them.
But artistry - in the form of intentional creative manipulation and alteration - causes the picture to deviate from this essential characteristic of photographs. As Hariman says
"The more they deviate from this requirement [i.e. indexicality], the more they become merely inventive, which is why fine art photography is inherently compromised: unlike the other arts, experimental optimization leads it away from its own medium."
In other words, the more radically creative you get in manipulating your digital pictures, the less photographic you become. Creativity in photography is thus circumscribed, and is subject to a strict discipline. Consequently, photography resembles the musical art of fugue or the poetic art of the sonnet or the haiku - it is a medium for creativity within tight constraints, and as such requires great skill. Thus, paradoxically, while the avalanche of "photographic art" is increasingly great, great photographs are ever rarer.