It's hard to know whether anything has been declassified, and you probably don't want to ask the question to someone in an official capacity. It sort of begs the question of were the the photos in your friends possession were ever classified? If they were, that puts things into a different realm.
My, now deceased, father-in-law was present at the Bikini tests as were hundreds of other civilian and military scientists. We have some photographs he took, though I've not seen any such as you describe. It's a safe bet that there are thousands of images of every aspect of those tests sitting around in family scrapbooks.
I agree with Wayne and Michael that as long as you have permission, etc. there should be no problem in publishing them. The only caveat I'd add is whether he made them in some sort of official capacity that made them subject to being classified. Once material is classified, it's subject to those rules of disclosure until the classification is officially removed. It really doesn't matter how much similar material is freely available from other sources, or, generally speaking, how old the material is.
I am not a lawyer either, but if your friends photographs fall into that realm of having been classififed, it wouldn't hurt consulting one who is knowledgeable of such things.