>so there is an argument then, in my view, that a film company's >indisputable copyright in a movie does not extend to each individual >frame of that movie. although each frame is a result of work it

Not true, at least in the US where all the images are explicitly protected by statute.  (See my previous post for citation.)  There's a historical reason for this in that the earliest films couldn't be copyrighted as a whole but instead the entire thing was printed onto paper and each individual frame was copyrighted as a still photo.  Of course this procedure hasn't been necessary for decades but there's no question that individual frames would be protected by copyright even if this statute didn't exist (unique expression, derivative use, etc).

The real question in regards to video grabs or frame enlargements is whether they fall under fair use and of course that will depend largely on the circumstances.  From the previous discussions I gather that academic use hasn't been considered in court but it seems likely this would be OK, the real sticker being how agressive the studio wants to be pushing the matter.  Print a frame from Snow White and you can almost certainly count on hearing from Disney; print a frame from Last Year at Marienbad and probably nothing will happen.

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Online resources for film/TV studies may be found at ScreenSite
http://www.tcf.ua.edu/ScreenSite