The copyright issue has gotten sticky with the internet. All too often, once something is digitalized it becomes almost impossible to control. Legally the original photographer still has the copyright, but many don't pursue the issue because of costs. One does have to be careful about posting copyrighted material, it could come back to bite you. I consider that when I submit photos to the forum. On the good news, US government publications aren't copyrighted, which includes the Army Signal Corps photos.
Gary B.