Though it tells you a lot about street art, structurally this documentary is about as anarchic as its practitioners are. Happily, “Exit Through the Gift Shop” is also as much fun as some of their work is.

The picture begins as a kind of overview of the form of extravagant graffiti that has taken on artistic pretensions, centering on figures like Los Angeles icon Shepard Fairey as seen—and filmed—by eccentric French transplant Thierry Guetta, a fuzzy-haired fellow who soon becomes the obsessive recorder of the artists’ activities. Guetta virtually ignores his business and family in order to take up his video camera and rush around recording the artists as they post their work under cover of darkness (and often on dangerous rooftops).

But Guetta refuses to rest until he bags the biggest of catches—the secretive British phantom known as Banksy. Fortunately, it appears at first, he gets his chance—through Fairey—and seizes it.

But it’s at this point, chronologically at least, that things shift. The artists begin to press Guetta to finish the documentary he’s supposedly been making about them, but in fact he’s just been shooting wildly, collecting tape upon tape but hardly watching, let alone organizing them. Now he’s forced to produce, and what he comes up with is a totally wacked-out edit that looks like the product of an ADD sufferer. Banksy decides to take over the film himself, and suggests that Guetta have a go at producing some street art himself rather than merely recording others doing so.

What follows in the last act is a film turning on itself as Guetta, who assumes the moniker Mr. Brain Wash, takes center stage in what becomes a wickedly funny commentary on the commercialization of the entire street art scene. Guetta goes into a productive frenzy, churning out imitative pieces in profusion. His greatest achievement, however, is in the area of (to use the words of an RKO Pictures executive explaining why the studio was dumping Orson Welles) showmanship instead of genius. Guetta mounts a huge debut exhibition in L.A. and promotes it with such fearless confidence, despite an injury that puts him in a wheelchair, that he becomes an instant star of the movement, prices for his pieces shooting into the stratosphere. Banksy is suitably appalled.

“Exit Through the Gift Shop” thus becomes less the celebration of street art it promises to be at first than an indictment of how the movement has lost its renegade soul in pursuit of profit—with the scraggly Guetta serving as Exhibit A. Of course one might argue that the reclusive Banksy’s cultivation of his mysterious image is as calculated as Guetta’s open drive for immediate fame, or even that the quality of his work is equally suspect.

But the fact that the movie encourages you to think about such things while enjoying the extravagances of people like Fairey and Banksy—and, ironically, the crazed excesses of Guetta—makes it, like the better pieces of the art it showcases, an oddity worth experiencing.