>isolated frame grabs are a minor element of the film, and in a form which
does not even represent >the film in the form it becomes an expressive work
entitled to copyright protection

Sorry but not true.  The individual images of a film are *explicitly*
protected by US copyright law.  See Title 17, Chapter 1, Section 106(5).
There are two separate issues here which are getting confused.  First is
whether frame enlargements or video grabs are protected by copyright, which
is clearly true.  Second is whether academic/critical use of these
enlargements/grabs are allowable by the fair use exemption, which is
probably true but will vary according to the situation.

Online resources for film/TV studies may be found at ScreenSite