Do you truly believe the prominent and extensive copyright information that accompanies a film doesn't apply to each and every frame in it? Why would one frame somehow be exempt from the copyright that applies to the whole film? It's not logical.
Making a painting from a photo or a film that isn't your copyright falls under the category of derivatives. It's a myth that changing 10 percent makes it okay, or that it's covered by fair usage laws. It's not a legal test, but I judge derivatives like this: if the painting and the photo were put alongside one another, would someone say the one was based on the other. If the answer is yes, then it's a derivative and you're on dubious ground.
There are other sources of reference material you could use without any copyright issues. Take a look at the photos on Flickr licensed with a Creative Commons copyright notice that allows derivatives asking for attribution only for instance; there are some fabulous things there.
Disclaimer: The information given here is based on US copyright law and is given for guidance only; you're advised to consult a copyright lawyer on copyright issues.
