Art is whatever you say it is. You can't define art. Any attempt to do so is an admission of your own lack of vision and creativity. Art isn't math or science. There's no checklist you can use to define it. There's no proof you can apply to qualify it. There's no test you can run to value it.
Now, just because something is art, doesn't mean it's good. And just because something is good, doesn't mean it's art. And just because something is good art, doesn't mean it's going to be recognized by the art community as such. In fact, most of the best art was widely panned during it's introduction, and only through time has it's importance and value been accepted. This is both liberating and debilitating to artists. Great artists don't always find recognition in their lifetime. Great artists don't always find recognition ever. And sometimes bad artists find recognition during their lifetime, and only to be eventually forgotten (Thomas Kinkade anyone?). So this allows anyone wanting to be an artist a valid reason to continue to pursue their vision even under the crushing weight of constant failure, and serves as a cautionary tale to any artist who may believe they have found success.
So, my point is, if you're trying to approach art like you would science, economics, or math, with rigid precision and dependable formulation, you will fail to understand it. You will only truly begin to understand art, what it is, and what makes it valuable, once you immerse yourself in it. And that process may take you a lifetime or longer. Art is the most difficult thing to understand that humanity has invented, and impossible to master. If you want a challenge, become a theoretical physicist. If you want a guarantee at failure where success can be crippling and humiliation can be liberating, become an artist.
Also, photography is a bad place to approach art from. There are no, and never have been, any great masters of art in the photography realm. There is no photographic equivalent to Van Gogh, Picasso, Michelangelo, etc. There have been some great photographers over the century plus that photography has been around, but there has yet to emerge a true master artist in the field. It's just too new of an art form. And I've found that approaching art is easiest through the masters. They're kind of the key that opens the door to that world.