In the case of People v. Enskat (20 Cal.App.3d Supp. 1, 98 Cal.Rptr. 646 (1971)), Enskat was arrested and charged with exhibiting obscene movies.  At trial, the prosecution did not introduce the offending movie into evidence, but instead offered a few still photos taken by police in the movie theater, as well as testimony by people as to how dirty the movie was.  Enskat was convicted, but the Appellate Court reversed, saying that in on obscenity case, the movie is clearly the best evidence and should be considered a 'document' covered under the best evidence rule. The prosecution had argued that the physical film itself was not the issue, but instead it was the 'projection of light on the screen' that defined the term 'exhibiting'.  Therefore the film shouldn't be considered a 'document'.  However, the Appellate Court found that argument to be unpersuasive. In this case, the reason why the prosecution didn't have the film was that the defendant still had it.  They could have asked for the film as part of discovery, and if the film was not produced, then that would be a good reason for using secondary evidence, and the best evidence rule would have been satisfied.