In the late 1800's cameras were quite different then they are now.
When you went to get your photo taken you would have to sit very still and hold the pose.
If you moved too much the picture would be fuzzy and ruined.
I guess this crazy idea of hiding the mom under a blanket so she could hold the baby still became the popular thing to do for a while.
It's a hysterical tradition really.
Umm...we can still see that you are there mom.
I think the pictures end up looking a little creepy.