They are usually oval, and if the frame is still around, they’re typically mounted behind a piece of convex bubble glass. The substrate they are printed on is a light cardboard which at least in humid Ferndale, almost always has some spotting.
This particular image had a rough life, with some water damage, a few tears, and a large portion was completely missing. Fortunately, the section missing was just the plane studio background and it was fairly easy to replace, keeping the texture and gradation present on the other side.
If you know more about these particular type of images were created, please drop us a line.