" A messy legal fight over copyrights to streetscape photos shot by a Chicago nanny whose life is chronicled in "Finding Vivian Maier," which is nominated for an Oscar on Sunday, threatens to slow or even stop new releases of her once-unknown work that has become a sensation only after her death. The enigmatic Maier died penniless five years ago with no will, no obvious heirs and no inkling that the more than 150,000 photographs she snapped in her spare time in Chicago and New York from the 1950s onward would become so prized.