Is it quoting or is it stealing? A noirish look at street artists

What's a painting worth? Like real estate and an athlete's salary, whatever the buyer is willing to pay.

Exit Through the Gift Shop is a beguiling and subversively funny entertainment that considers art's worth from many angles, including that of guerrilla painters, gallerists, and seasoned collectors.

The film is directed by and features Banksy, pseudonymous street artist and provocateur, notorious for his 2004 forgery of British banknotes that swapped the queen's image for that of Princess Diana. (Rather than "Bank of England," the imprint on the bills read "Banksy of England.")

So it is altogether possible that Exit is a cinematic forgery. Whether it is a documentary or a punkumentary, who can say? Not even its distributor knows for sure.

Yet as it follows the stealth artmaking of taggers who by night surreptitiously stencil, paint, or otherwise affix images to walls and lampposts, it establishes a noirish mood and thriller uncertainty that keeps the viewer engaged. And off-balance.

Who are these artists from London and Los Angeles using the city as their canvas? How do they elude the authorities? How do they support themselves? As the film suggests: because they can, because they must, and by selling "props" or other residue of their urban theater.

In the cinematic adrenaline rush, narrated puckishly by Rhys Ifans, Banksy appears on camera, his face obscured by a hoodie and his voice digitally doctored. He's not exactly a masked man.

But like the Lone Ranger or Big Brother, the British-born artist derives his power from his anonymity. As he tells it, he wanted a documentarian to make a movie about street art, but instead the street artist ended up making a movie about the documentarian.

That would be Thierry Guetta, also known as Mr. Brainwash, a French expat and thrift shop mogul in Los Angeles. Guetta, who makes his money by selling odd lots of clothes and calling them "vintage," is a hippie throwback "with facial hair from the 1860s" - as Banksy nicely describes his muttonchops. The Frenchman is addicted to two things: videotaping and thrill-seeking. The two habits converge when he documents the work of his cousin, Paris street mosaicist Invader.

One guerrilla leads to another. Which is how Guetta comes to hook up with Banksy and Shepard Fairey (a stenciler not yet famous, as of the film, for his Obama image "Hope").

Soon Guetta becomes their Virgil, guiding them to blank walls in the Inferno of Los Angeles. At the same time he is their Boswell, diligently chronicling their improbable artistic exploits (including a Banksy incident at Disneyland) while detonating graffiti bombs of his own.

This initiates a role reversal in which documentarian becomes artist and vice versa.

Banksy contrasts the footage from his circusy 2006 "Barely Legal" exhibition, notorious for a live elephant in the room, with that from the 2008 "Life is Beautiful" exhibition by Mr. Brainwash (Guetta's nom de rue).

Guetta's work is like a Xerox of a photocopy of a mimeograph of a 1965 Andy Warhol show. And its silk-screens of Arnold Schwarzenegger in a Marilyn Monroe wig immediately attract collectors, despite the arbitrary pricing. According to Artforum magazine, in two weeks Guetta sold more than a million dollars worth of work.

When Banksy uses imagery from other artists, he assembles it in a meaningful and original way. When Guetta does the same, it looks meaningless and derivative. Is Banksy suggesting that, artistically speaking, he quotes other artists but Guetta plagiarizes? And that Guetta is repackaging images as he repackages odd-lot jeans and T's?

The contrast between the two exhibitions is so neat that it has led many to conclude that if Guetta didn't exist Banksy would have had to invent him. Maybe he did.

Banksy's film raises disconcerting and compelling questions about the authenticity and value of contemporary art. "It's not Gone With the Wind," Banksy wryly observes. "But there's a moral here somewhere."

It's a moral straight out of The Maltese Falcon: As Sam Spade might observe of Guetta, "The cheaper the crook, the gaudier the patter."EndText