Exit through the Gift Shop is a halfway engaging, halfway aggravating documentary on street art and its inevitable commercialization. Signed by the pseudonymous Banksy, a British graffiti artist who zealously guards his true identity (“The Scarlet Pimpernel of Street Art,” as one newspaper headline puts it) and who appears here on screen wearing a hoodie in silhouette or with his face digitalized, the film ostensibly began as the work of Thierry Guetta, a muttonchopped French émigré who operated a vintage clothing store in L.A., became an obsessive amateur videographer, trained his camera in particular on the activities of guerrilla artists, turned himself into one of them under the moniker of Mr. Brain Wash, and ostensibly edited his footage into an unreleasable mess, at which point Banksy ostensibly took over the project, utilizing and supplementing Guetta’s footage, whipping it into the present shape. We must keep saying “ostensibly” because — well, who knows? Anonymity is not a trustworthy persona for a documentarist, especially one with a prior reputation, a prior rap sheet, as a prankster. (Nor does the irony-dripping narration delivered by Rhys Ifans inspire much confidence.) Whatever the provenance or purpose, we have here a lot of footage of street artists in action, poor in quality but sufficient in quantity to enable us to gauge the range of cleverness, and to think our worst thoughts about the impact of money and hype in the art world. “Anthropologically, sociologically,” remarks street artist Shepard Fairey, a/k/a Space Invader, who could be talking about the film itself, “it’s a fascinating thing to observe.” Artistically, aesthetically, it’s a confounding thing.