I wouldn't waste my time using a digital camera to photograph old photos. You have to have it on a copy stand to be sure the focal plane is correct, and no matter how you have a digital camera set, the outcome, once you dissect that mess of images, they're going to be lower resolution and you're dealing with the peculiarities of an extra lens (the camera's).
It's also more bother to load them out of the camera and adjust/crop them apart than it is to scan them directly into something like Photoshop and into a durable format. I sincerely doubt that the Library of Congress would recommend that camera method over that of a good flatbed scanner. If this were the case, the Special Collections folks at the library where I work (and they regularly scan images for me) would be buying cameras. But they're not, they're buying bigger and better scanners and sophisticated software to work with the output. FWIW