Photography is, maybe, unique in that one can reasonably disagree with the author on what a piece means. That is, without deploying the unusual methods of literary criticism or something similarly antic.
If I write on a piece of paper my dog is happy the meaning of that piece of paper is pretty clear. A po-mo lit-crit aficionado might remark that, by pointing to the dog's happiness, I allow the possibility of the dog's sadness and that therefore encoded in my piece of paper is the dog's sadness as well. Which, well, ok then. Normal people will agree with me on what it means, most of the time, though. Note that the dog's actual joy is not relevant here. Perhaps I don't even have a dog. The point is the meaning of the text on the paper.
If I make a painting of my dog, larded up with cues as to the dog's joy, and maybe even title it my dog is happy then again the meaning is clear. You might remark that the body language of the dog in my painting is not consistent with joy, but that just makes it a bad painting (maybe). The meaning of it is still clear, it is an assertion about my dog's happiness, and there isn't much room for disagreement. The meaning of the painting is unambiguous, and disagreeing with me, the author, on what it means is going to be a bit dicey.
Now let us say I photograph my dog, again larded up with the tells of canine joy. The ball in flight, the bounding animal, whatever. Perhaps I entitle it, again, my dog is happy. Whatever is necessary for you to imagine that my intention is clear, imagine it.
This thing, you can trivially disagree with without any lit-crit shenanigans.
If the dog's body language indicates that it is anxious rather than happy, there it is. You can point to that, and say "no, the meaning of this picture is not that the dog is happy, but that it is anxious, you have misread the dog."
Again, it's still not the actual joy of the dog we're interested in here, it's what the meaning of the piece it. The picture's meaning is, as we see it, contrary to the author's intention.
What drives this, obviously, is that the dog's actual condition is (or at least might be) robustly encoded in the picture. It's right there, you can see the dog's state of mind in the set of its ears, its jaw, its tail, whatever your book on dog body language says.
The distinction here, as I see it, is that when I make a painting or write some words, every smear of paint and every letter on the page is laundered through my psyche. I might lie to you about my intent, I might be unconscious of my intent, you might misread my intent. But my intention informs every infinitesimal blotch in the thing. A photograph, on the other hand, is not made but selected, generally from reality. My intention informs only the rough form of the thing, my intention informs the moment and the angle, a few other parameters, but in the end the real world remains traced there in the picture.
The author is not really in control of the meaning of a photograph. Meaning arises both from the real world shown in the frame, from the viewer's perception of the real world, and often only in third place, the author's intention.
One of the virtues of the book form, surely, is that there are more places for the author to stick their oar in and control what the hell is going on.