Why would Shepard Fairey, or any other artist, want to copy an image that is already out there and claim it as his own? Why would he think he could get away with it? Forget, for the moment, the legalities: The laws governing intellectual property rights are, after all, devilishly complex. And put aside, if you will, the unrelated issue of whether Fairey deserves to be arrested for vandalism. We can leave that to the defenders of private property - self-appointed and otherwise. It's a serious issue; speaking as a disinterested aesthete, I would only say that, for the most part, I'd rather look at Fairey's attractively designed posters than the brain-pounding ads for fast-food outlets and failing banks that currently dominate the urban environment. Indeed, being in a room filled with Shepard Fairey's images - as is possible during his current Institute of Contemporary Art show - makes you immediately aware that he does more to transform the images he appropriates than many are prepared to acknowledge. The famed Obama poster may well be based on a crisp but generic-looking image by an Associated Press photographer; but Fairey has done so much to it - from its underlay of newsprint and decorative patterning to the coloring and its distillation into a simplified graphic lan guage based on sharp tonal divisions - that the resemblance is barely relevant. Artists have copied other artists, of course, since time immemorial. Rubens copied Titian, Manet copied Velázquez, Cézanne copied Manet. In most cases, they were motivated by the desire to learn, or to pay homage. In the modern age - what the philosopher Walter Benjamin famously called the "age of mechanical reproduction" - images flooded the public sphere as never before. If, in the past, artists had looked out the window and seen a rural or urban landscape and been inspired to represent it, they now saw - yelping for attention and crowding out trees, bricks, and mortar - advertisements, typography, banners, flags, and a vast array of other signs. All this artists treated as subject matter. How could they not? Just like landscapes in nature, these urban, signposted landscapes were internalized, so that the exhortations to commercial exchange or political engagement they carried became part of artists' mental landscapes - nourishing memory, longing, hope, obedience, rejection, irony, and every other kind of human response. Throughout the 20th century, the world of signs continued to proliferate. When, in 1954-55, Jasper Johns painted an American flag in encaustic over newspaper - just the flag as a graphic arrangement, nothing else - and presented it as his own work of art, he was not the first to treat flags as visually appealing subject matter: Manet, Monet, and Childe Hassam had all been there before him.

But, by taking the flag out of any "natural" context and treating it as a sign - a sign, and also, confusingly, a thing - Johns was taking the next logical step. At once mute and full of mystery, Johns's flag had something arbitrary about it. Like his paintings of targets and numerals, it seemed to have been plucked at random from a network of signs so charged and confusing that one's ability to pin it down to any particular meaning teetered on the verge of collapse. Johns's flag chimed with people's experience of living in a world saturated in signs, but also longing for authenticity. Along came Pop artists like Andy Warhol and Roy Lichtenstein - both of whom routinely crop up in discussions of Fairey. Both treated preexisting images (comic strips in Lichtenstein's case; advertisements in Warhol's) as objects of wit and ironic play in ways that many found enormously appealing. Their work reflected an increasing savviness about visual signs on the part of the public - an ability to read them with skepticism and detachment even as one was seduced by them. Many accused the Pop artists - and especially Warhol - of nihilism, and understandably so. He favored highly charged subject matter (celebrity portraits, race riots, electric chairs) but his attitude was frustratingly amoral. Crucially, though, Warhol had perceived something fundamental about imagery in the contemporary world - something that distinguished it, at least in degree, from language: that despite its great impact, it was slippery, and infinitely exploitable. In the '70s and '80s, a group of artists known as "The Pictures Generation" (an exhibition about them is opening at New York's Metropolitan Museum of Art in April) began appropriating imagery found in advertising, film, and the art world in a more wholesale fashion. Looking around her, one of them, Sherrie Levine, found the world "filled to suffocating. . . . Every word, every image, is leased and mortgaged." These artists were putting the very possibility of being original in doubt. Levine is best known for re-photographing Walker Evans's photographs from a catalog and presenting them as her own work (Evans himself, let's not forget, became one of America's most celebrated photographers in part by photographing preexisting signs). Another member of the Pictures Generation, Richard Prince, re-photographed images from Marlboro ad campaigns, blew them up, edited out the advertising copy and the surgeon general's health warning, and presented them as his own work. Given the current local brouhaha over Fairey's appropriations at the ICA, it's interesting to recall that the first serious overview of the Pictures artists was at the ICA in a 1986 show called "Endgame: Reference and Simulation in Recent Painting and Sculpture." All of the Pictures artists were hyper-alert to the ideological implications inherent in imagery. In this, they were deeply influenced by Continental thinkers such as Benjamin, Roland Barthes, Guy Debord, and Jean Baudrillard. With irony and parody as their tools, they believed they could "hijack" certain kinds of ideologically loaded imagery to create messages of insubordination or resistance. Many chose to display their protest art in public spaces rather than art galleries, which they saw as compromised or cut off from the broader public.