Some features of instragram I guess was based on this practice years ago.
It's called TTV or through the viewfinder.
You find a camera with a glass finder (kodak duaflex or argus seventy five),
make a contraption to stop the outside lights spoiling the finder, place
a camera on top and voila! an image with soft vignettes and some natural borders.
Images were made using a point and shoot digi and Argus 75.