Their pro-Obama work — there is no similar phenomenon for John McCain — has been spotted everywhere, even Paris and Beijing.

On a brick wall in downtown Atlanta that usually is splattered with graffiti tag names, a spray-paint portrait of Barack Obama now gazes over the streetscape.

In Chicago, an abandoned warehouse on the city's South Side displays a life-size silhouette of the Illinois senator, microphone in hand.

And all over Los Angeles — on stop signs, underpasses, buildings and billboards — hundreds of posters and stickers of Obama, emblazoned with the word "Hope," have been slapped up, guerrilla-style.

This year, some of the most arresting images in the race for the White House are not the work of ad agencies, political consultants or photojournalists but of a subculture of artists who use the streets as their canvas. Their pro-Obama work — there is no similar phenomenon for John McCain — has been spotted everywhere, even Paris and Beijing.

It's an odd twist in the world of street art, an arena where creative renegades question power and convention with homemade posters and hand-painted murals — and don't usually endorse major party politicians.

"It's not cool with the sort of rebellious, punk, street-artist types to support something that is seen as a part of the system," said Shepard Fairey, the Los Angeles-based street artist responsible for the "Hope" posters and stickers.

Yet when it comes to Obama, street artists are falling into line. "Obama's a rock star; he's got a great brand, and he's a very sexy candidate," said Ian Bourland, a University of Chicago graduate student who is one of the few academics studying recent street art. "It's his race, his politics and his charisma."

Street artists embrace the presumptive Democratic presidential nominee's experience as a community organizer, in part because they view their own movement as similarly grass-roots. "He's perceived as sharing their ethos," Bourland said.

Fairey and Chicago artist Ray Noland are in Denver for the Democratic National Convention as part of the Manifest Hope Gallery Contest, a national art competition. Artists were asked to submit work about Obama or centered around the themes of hope, progress, change, patriotism or unity. The best works are on display at the Manifest Hope Gallery in downtown Denver.

Street art — regarded as creative, non-gang graffiti by its admirers and as vandalism by its detractors — evolved in part out of the do-it-yourself punk movement of the 1980s.

Current targets of its rebellious edge include the Iraq war and gentrification, along with old enemies such as capitalism. "It's pretty unusual to find things that street artists and graffiti artists are in support of," said Joe Austin, a University of Wisconsin history professor who studies youth movements.

Still, street artists such as San Francisco's Eddie (he asked that his last name not be used for fear of legal retribution) are enthusiastic about Obama and say they are expressing their sentiments in the vocabulary they know best.

"I could go and volunteer at the campaign and make calls, but that's probably not the best use of my skill set," said Eddie, who has plastered the Bay Area with red-and-black posters that feature a close-up of the candidate's face. "Street art is what I do."

Noland, 35, also a freelance graphic designer, makes Obama posters filled with basketball imagery to appeal to urban youth. In one, a smiling Obama clutches a red, white and blue basketball and stands beside the slogan "Obama got next" — a play off the lingo basketball players use to claim a court.

Noland became interested in Obama while reading his 1995 autobiography, "Dreams From My Father." "I thought, 'This guy has got it all. He's got the pedigree. He's gone to Harvard, but he's also connected to the community, to the neighborhood,' " Noland said. "He also plays ball!"

His art is, Noland said, "a conscious effort to position Obama in a certain way, to position him as cool and to position him as hip."

Noland first sold his posters to friends. Then, just before the Illinois Democratic primary, he rented a storefront and made it a temporary art gallery, where he marketed his screen-printed Obama posters and paintings. He eventually packed the pictures into his Subaru and took his work on the road. Noland set up shop in Pennsylvania, North Carolina and Oregon for those states' primaries.

In North Carolina, Noland was surprised by a visit from Obama and his wife, Michelle, who "spent all of this time just gazing at the images," Noland said. "I think he was overwhelmed at seeing all of this work with his face all around." But, Noland said, Obama told him to keep up the good work.

The pro-Obama street art movement has its detractors. Other artists have defaced the Obama work, and one blogger attacked Noland for depicting Obama "as a Messiah figure."

Noland said he understands the critique — in one of his early images, Obama seems to be emanating gold rays of light — and he has toned down his recent work. Other critics have dismissed Fairey's Obama "Hope" image, an idealized portrait of Obama gazing toward the sky, as no more than propaganda.

Fairey, 38, admits that his design was inspired in part by Soviet propaganda posters, but he insists that it is meant to provoke, not indoctrinate.

Fairey got on board with Obama in 2004, when he watched the senator's televised speech at the Democratic National Convention. "I was so impressed," he recalled. "I thought to myself, 'This is someone to watch.' "

He liked Obama's emphasis on the environment and his commitment to curbing lobbyists' power. So in January of this year, just as the primary season was heating up, he drew up the design for the "Hope" poster. He has distributed more than 80,000 of them and made a downloadable version available free on his Web site.

Fairey, who has been arrested multiple times for trespassing and vandalism while putting up his guerrilla art, was worried that Obama's campaign might not want to be associated with street art.

"When you look at how the general public looks at (street art), they're scared of it," he says. "They associate it with gang-bangers and anarchists."

Yet in February, Fairey received a letter signed by Obama that thanked the artist for his support and declared, "The political messages involved in your work have encouraged Americans to believe they can help change the status quo. Your images have a profound effect on people, whether seen in a gallery or on a stop sign."

Fairey also was asked to donate an official "Hope" campaign poster, which is being sold on Obama's Web site.

And with that, the renegade went mainstream.