Craft is something performed with a known outcome and skill which guarantees that outcome; such as the building of a chair or the putting in of a window. Art, on the other hand, is the expression of human vision or emotion, the outcome of which is not always a guarantee. Art, as Kant said, possesses a certain "genius" or infusion of the spirit which craft does not have. Though art benefits when one knows craft (say how to use paints) knowledge of craft is not necessary for doing art. W/o the infusion of genius, however, craftsmen can do their job quite well. So it seems that art isn't so much a "what does it do" question as a "how is it done" question. If the object produced is one which was achieved knowingly with a guaranteed outcome (as in, this will reroute the sewer) it is craft. If it is produced such that the outcome is not entirely known, yet the work is infused with the indescribable element of genius, it is art.
Do I agree with this?
Yes and no. It seems plausible enough and seems to be extolled by such greats as Kant and even Plato in the Republic; yet I do think that there is a craft to art which can also produce an outcome knowingly. Certain images or forms do certain things, or strike us in a certain way. Colors affect us, images affect us, notes affect us in a fairly consistent manner. Thus the artist, although expressing genius, does so with a knowledge of how his creation will affect others; in other words, he knows what could convey his vision effectively (instead of just trying things until they work). This, of course, is the skilled artist not the hack.
So what is art? To give a criteria by which we say "this is, this isn't" I think is near impossible. Art is the expression of the human soul, the trying to recapture lost paradise, the visions of the beautiful and the damned. How that plays out defies definition. There are some things, though, that work and make us say "yes, that is it" and others that do not work at all and leave us disgusted and flat.
Perhaps, then, the more important question than "what is art?" is "what does art accomplish?" Do artists just produce stuff haphazardly to satisfy themselves in an ars gratia artis way? Do artists produce for cash only? Do artists seek to alter their audience and in what way? These, I think, are more engrossing questions that what the thing is. Ultimately, ars is simply that; literally "a making"; what the Greeks called "poiesis". It is the thing we do that no other animal does. In itself neither a good or evil. But in how it is made and what it seeks to accomplish, therein lies the good or bad art.
BTW, great article on ars and techne by Christopher Janaway entitled "Arts and Crafts in Plato and Collingwood" here at JSTOR if you can access it.