When my grand parents had their wedding picture taken, it was a stiff and no grinning. Most likely because they either had terrible teeth OR the camera lens was very slow and if they moved from that statue state the picture would be blurry.
My parents had a grin.
With technology of the day, lots of pictures are posted. They are not stiff nor grinning. Many of the pictures have all sorts of tongues sticking out, fingers pointing to themselves, crossed eyes, and of course lots of drunken pictures.
Perhaps pre-digital, we didn't use film for those poses. Perhaps we liked pictures with a message. Perhaps we thought. In thinking about the 2,500 or so pictures of my own children, I don't think there is one tongues sticking out, fingers pointing to themselves, crossed eyes, and of course lots of drunken pictures although there may be a couple of 'rabbit ears' photos.
When these early twenty people have children and they ask, "What is this about Mommy"? Mother will have to say of her cross eyed, tongue out, finger pictures, oh, Mommy was really drunk on all of these pictures and when you grow up, you can do the same.