I have previously posted about ShotDeck, but it is a paid site, while I didn’t know about FilmGrab which is free. You can grab iconic images from films as reference shots, which can be very useful.
It claims to have 2500 films with 160K hand picked images.
Playing with it a bit, it is good, though could use a search versus just brows by film artist and category, but that is only a minor gripe. Well worth checking out.