We could probably fine-tune a tiny convolutional neutral net image classifier and just hold on the last good frames for longer to cover the frames with clear trolling and nsfw images.
I think it would be subtractive. To my eye, it seems like the point of the project was to celebrate the free expression of the crowd. The lack of censorship and filtering is core to the purpose of the project. If you start filtering out individual contributions in order to more accurately reconstruct the original movie, then I don’t really get why you wouldn’t just pirate the movie.