Irritatingly, while they say that there are over 7 million photographs, I couldn't see how to access any of them, which was irritating. It's only when you've viewed an image that you get to see the stills from the clips themselves that you can purchase. They are royality free, but you do have to pay for use from a couple of dollars upwards.
It's an interesting collection, and if you're into US history from the 40s, it's made for you. Other people may have rather slimmer pickings though.