A tattoo is very much art. That is like saying that Don Quixote by Picasso doesn't qualify as art because it is nothing more than a doodle. Art can be anything. Look at Black Square by Malevich, Composition with Red, Yellow Blue and Black by Mondrian, or even Warhol's Campbell's Soup Can series. Duchamp's Fountain was probably the biggest snub against the pretentiousness of art critics. I have even seen that work in person along with canvases by Van Gogh, Rembrant, Monet, and many other names that people immediately recall when you say the word "art". A tattoo artist has as much validity as an artist as Michelangelo. The differences in the medium, the style, the time period, the (arguable) talent, etc. are apparent, but each fits into the definition of producing "the conscious use of skill and creative imagination especially in the production of aesthetic objects".