Couldn't the Mickey Mouse image be protected as trademark (which is infinite, as long as it is defended)? Even if the old films fall into the public domain, Disney could use trademark to keep people from creating new non-approved films.
I've argued this point with friends for years. Individual characters (Mickey Mouse, Bart Simpson, James Bond, etc) and the like would be trademarked, and could only be used in new works by the trademark holder. Those works, however, would be released into the public domain after x years.