Well, "art" is usually pretty subjective. As they say .. beauty is in the eye of the beholder. However, I think there are basic rules that render photos either aesthetically pleasing -- or not. I'll give my opinion here about what is pleasing to MY eye, along with some constructive criticism regarding composition.
Photo #1. .. I agree with storyist. But oftentimes, camera angle can make a world of difference. Instead of the typical head-high camera position looking down at the dog, try lowering the camera so that it is looking slightly up at the dog, or perhaps only very slightly down. Adjusting for less angulation might improve this type of picture.
#2. .. Nice. Although cropping out about 10% (?) of the entire left side of the pic might bring better balance. I would aim for equal 'weight' of the straw-coloured background, regardless of where the dog itself ends up being positioned. As is, there seems to be too much weight to the left, especially with that tree line coming in from the left side as well. Centering the dog's head, for example, with his body off to the right, usually creates an odd looking picture.
#3. .. I'm ok with the black & white, but including the dog's legs and feet in the shot would greatly improve the interest. Also, collars and tags very much distract the eye to those items. Remove them if possible for the sake of cleanliness. I do like the pitch-black background here.
#4. .. Beautiful !! Not much to be critical of there.
#5. .. I like the b&w, I like that the camera focus is on the ball and the dog itself is out of focus. And I love the artistic nature of the shot. While it isn't a dog picture per se, it tells a great story. IMO, with that particular focus / non-focus, it's truly a matter of art imitating life. ie: the dog's focus is on the ball, the same as the camera is. Only criticism here is that the dog's entire body (front feet) should also be included in the frame. And maybe crop a very small amount off of the right side of the pic.
#6. .. See the tree that stands alone on the horizon with a bit of a V shape to the trunk? .. I would crop it just to the right of that tree, for balance. I would also remove the dog's leash and collar (if possible) prior to the shot, in order to keep the details clean. I find the leash itself to be quite a negative impact to an otherwise free and wide-open feeling.
#7. .. Once again, I think cropping would really improve the overall look of this picture. Roughly about 20% off the left side should do it. I like the angles of the waterline, the top of the tree line, and also like the somewhat distorted reflection of the dog in the water.
#8. .. From an artistic perspective, THIS one is my favourite by far. Balance is perfect. Subject matter is perfect. Colour scheme is perfect. It tells a wonderful story of two apparent siblings, each with vastly different motives, and different individual focus points. Simply WONDERFUL !!
#9. .. Nice. Although I do find the rope toy and diagonal twig slightly distracting. Otherwise, balance / composition / detail / expression etc are all good.
Attachment. .. I dunno, There seems to be something missing in the composition. I love the dog wrapped up in a blanket keeping warm, with a relaxed and comforted expression in his eyes. But for me, there's something lacking in the choice of background. 'Cold green' siding just doesn't set this one off.
So anyway, there you have it. My UNPROFESSIONAL opinion. Hope it helps.
Keep up the good work, and best wishes for all of your future photographic endeavours.