I know my own search for "royalty free" photos can get tough. I mean there tons of sites, but it can get murky. I don't know how much is in your budget for legal advice, but I would at least gather the links to the sources (writing them down, whatever), and seeing if you can get some basic advice from a copyright lawyer for an affordable price(may be an oxymoron. Some lawyers for a hundred bucks or so will sit down with you for an hour and tell you what you can and can't do).
Best case, apply to all for permissions, and see who responds positively.
I sometimes think with docs like this, it's not the filming or compiling that takes the biggest amount of time, it's actually getting your legal ducks in a row before it goes public.
It's interesting how the amount of people on the internet, accessing millions of photos, movie clips, ect, is forcing more people to take a look at exactly what you can and can't do with copyright.
I know myself, I am writing a book about masks that will (hopefully) be a nice coffee table book with pictures. I can save an image from the internet and post it on manuscript(that is totally offline). I'm doing this as a kind of mockup. The FUN part will be if/when I decide to publish, I'm going to have to track down the source of each of those photos. Are they public or private? Is simple "permission" enough for them, or do they want money? Does it fit into the "fair use"category? If I ever want this book to get out and be purchased by people, I'm going to have to dot my Ts and cross my I's legally.
While the internet has been a blessing for access, its also been a real headache for people involved in copyright(except the lawyers, they are making scads of dough!
), with a picture or film grab just a mouse click away.