For me, art is an act of communication, usually between humans. The communication has special qualities: it is usually of a more sophisticated quality than ordinary communication (though what counts as sophisticated is a matter of debate). The sophistication should indicate some amount of thought or skill on the part of the artist that most people don’t have.
In addition to sophistication, there are a lot of people who would also add the criteria that the art must also be beautiful. I do not hold with this, but I point it out, because I think it is important to include it as part of the discussion.
In my definition, art is a dialogue between artist and perceiver of the art. If no communication goes on, then it isn’t art.
Where I am uncertain is if it can be called art when the communication is between humans and non-humans. I go to Yosemite, and there is beauty everywhere. One could consider Yosemite to be an act of communication between mountains and trees and rivers and human. In this, the perceiver, the human, is the only one who, apparently, can manipulate symbols. So a kind of reduced dialogue happens.
We are uncertain if the artist is doing things intentionally to communicate to us. And yet, we are part of nature, and we are evolved to find nature beautiful, and thus to treasure it (see how well that works!) to some degree. Certainly, in our representations of things, it is popular to represent nature.
Still, nature is like “found” art. Just as the photo of Nimis’ wall, and Harp’s perception of his tofu. In doing this perception, they might keep their observations to themselves, in which case it is not an act of communication between humans. However, the instant they talk or write about it, we start to imagine it, and, it seems to me, it becomes art.
All writing and all words are attempts at communication, so is everything art? Well, I believe there is art in everything, but that doesn’t mean everything is art. There is a kind of intentionality to art: it means going beyond the ordinary, in some way. Yosemite is beyond the ordinary natural setting. Nimis’ wall is beyond the ordinary wall. Harp’s tofu is, in his opinion, beyond the ordinary skillet of tofu (I bet he has an awesome kitchen). And I’d like to think that my words would also qualify as art.