Teri Horton (pictured), a 73-year-old retired truck driver, paid $5 at a thrift shop for an ''ugly'' spattered canvas that may be a Jackson Pollock. Is it? That's the mystery of this beguiling documentary detective story, Who the #$&% is Jackson Pollock? Horton's attempt to authenticate the painting in the face of a hostile art establishment becomes a study in forensics, taste, money, and class warfare. A fingerprint is found on the back of the painting, but does that mean it's authentic? My theory: Yes, it's a Pollock but it's a bad Pollock, which is why art-world snobbery became aesthetic myopia.