It appears to be an older generation Smith & Wesson 915 automatic 9mm.
I'm basing this on the simple rear sights, which the similar S&W 5904 doesn't have (they use the standard sights with "ears" or Novaks), and since the trigger guard is squared off, it's likely an earlier gen model.
To note, the image is reversed, as is typical of film posters.
__________________
|