drngr said:

Reegar said:

Sherlock Holmes is public domain. Sherlock Holmes starring Robert Downey Jr. is copyright.

Which would be a good point of reference if we were discussing an entirely new movie based on Night of the Living Dead.

The RDJ SH isn't a bad point of reference, because that's what's called a derivative work. It uses a public domain setting, characters etc and creates a new work (it could've been even a straight-up adaptation of the stories) based on them.

http://www.legalzoom.com/intellectual-property-rights/copyrights/what-are-derivative-works-under

Night of the Living Dead is actually an interesting example. The movie itself is public domain, but as far as I can tell (someone correct me on this if I'm wrong) not every version of it is public domain. If you were to, say, buy the restored BD version of it and post it online you might be breaking the law, because the alterations made to that version might constitute a "derivative work". That may be the reason why there's so many different cuts, versions, colorizations etc floating around. It's just people grabbing free stuff, making money off of it and protecting their asses.