It's a very time consuming job, for I have to watch a movie frame-by-frame to create the movie stills I like best.
The complete process of capturing a movie and publishing a selection of the screenshots takes me about seven days (40-60 hours) per movie.
Personally I love to capture facial expressions ('micro expressions'), details and plot development. But visitors regularly ask me to also capture a wide range of other moments, for instance:
make-up artist like to see closed eyes, set decorators like to see overall sets, (wannabe) directors ask to show different used camera angles and so forth.
Others ask me to pay special attention to cars, weapons, boobies, feet, an actress smoking, jewelry, paintings/pieces of art, clocks&watches, weapons and an endless list of other details. So I try to include a few of those too. Can't please everybody, but am doing the best I can.
I also publish screenshot collections created by players of my MovieQuiz blog.