Recently I have been researching Victorian photography, in preparation for my latest ebook: Fingers and the Dream Thief.
This is the object that I was searching for. It is called a posing stand and it was used in Victorian photography. Early in the history of photographic development, chemicals were not sufficiently sensitive to capture an image without using a prolonged exposure of several minutes. Therefore, this device was required.
Imagine how difficult it must have been for a subject to maintain a rigid pose for several minutes, without the slightest movement or tremor. The posing stand was set up behind each subject. Then they were clamped into position, so that they could stand and maintain a given pose for a sufficient time.
Although they look like gruesome items of torture, these innocent posing stands were commonly found in photographic studios across the world and would have been in fairly standard use. Sometimes these were not hidden carefully: when you look at many Victorian portraits you might just notice the remains of the stand behind the feet of a subject.
Incidentally, the long shutter speed also explains why Victorian subjects look so stern or depressed in family portraits: it is simply impossible to maintain a smile for longer than a few seconds without severe facial discomfort. How long can you maintain a full beaming smile? (I managed 35 seconds.)
However, I do find these stern-looking Victorian photos incredibly elegant and attractive to view. If the subjects were smiling broadly and dressed more casually, I am sure that they would lose their professional pleasing appeal.