IME, most natural history museums have no problem with cameras. Ask, if you're unsure; most of the time, cameras are welcome. Sometimes, if a fossil is very fragile, they request no flash photography. But otherwise, you can take as many photos as you want. I have tons that I took at the Museums of Natural History in New York and London. Including some of the feathered dinosaurs from China. (No flash allowed for those, but they came out anyway.)