"It represents something I have never seen, have no concept of, and yet I have to form an abstract notion of what is presented?" - Oscar.
Only if we start from the premise of having to represent something specific, or the spirit (mood) thereof. I prefer to leave it more open than that, the idea being that if the combinations of shape, colour or lack of it do something to me, in the sense of creating a sense of mystery, and I'm not sure why because they don't represent a specific, then that's abstract: the image is the essence of itself.
In fact, if the abstract is a photograph (a photo, and not a PS construct) it has to have an original, physical genesis where a painting does not; if that original is not discernable, then perhaps I deem that a better abstract, if only because it leaves me guessing. But I will only be left guessing if the image moves me; otherwise I simply won't care, which in my eyes, marks it a failure, even if my own creation.
"But that, of course, can be considered a case of the tail wagging the dog. If we are trying to communicate something with an abstract photo, then clearly, that type of abstraction should fulfil the former definition more than the latter." - Oscar.
But why assume the dog needs a tail? Why should an abstract try to communicate something specific? Isn't it enough that the thing excites, possibly even because of its mystery provenance? As long as the dog has a healthy bark...
"Doesn't happen. What does happen is that the texture and color may evoke a mood, for each viewer differently." - Oscar.
Which is where I came in.
;-)
Rob