You know, I don't know. I assume they kept them in some sort of photo book. I'll have to do some more research. They also, as yachiru pointed out below, took pictures WITH the dead people, sometimes dressing them and sitting them for the portrait as if they weren't dead at all. I have one saved away in the Collect Your Courage tumblr of a man laying in bed next to his dead wife. It's morbid and fascinating and I can't look away EVEN THOUGH I HATE DEAD PEOPLE.

And from what I know, the mothers are not actually supposed to be in the photos, they wanted photos of just the children but it was hard to get children to sit still long enough to be able to get a good photograph, so they would hide the mothers and let them sit and hold the children still. That one's not nearly as creepy after the explanation. It makes perfect sense. It just makes for weird fucking photographs.