The 1940s Columbia movie serial that is. It’s available to view over at the Internet Archives. I knew that the 1940s Superman cartoons were Public Domain, but I was not aware that this motion picture serial was also in the public domain. The Archive describes it as:

The Superman serial was a 1948 15-part black-and-white movie serial starring an unaccredited Kirk Alyn (but billed only by his character name, Superman) and Noel Neill as Lois Lane. It is notable as the first live-action appearance of Superman on film and for the longevity of its distribution. The serial was produced by Columbia Pictures, directed by Thomas Carr (who later directed many early episodes of the Superman television show) and Spencer Gordon Bennet, produced by Sam Katzman and shot in and around Los Angeles, California. The series was originally screened at movie matinees and after the first three scene-setting episodes, every episode ends in a cliffhanger. The Superman-in-flight scenes are animations, in part due to the small production budget

[via Boing Boing.]