A lot of things in the world is in reality old news; like hidden photography, to name one! Stirns hidden camera was produced by Rudolf Stirn in Berlin between 1886 and 1892; at a time where a man's attire naturally, and necessarily, consisted of a vest. Stirns flat camera was slipped unnoticeably in under the vest, with only its lense discreetly peeking out through one of the buttonholes. The camera was held in place with a strap around the neck.
Through another buttonhole you could grab hold of a mechanism, turning the glass plate inside the camera around. The glass plate was as round as the camera itself, measuring 14 cm across. The plate could fit up to six images, each 4 cm wide. The exact number of cameras sold is said to have been around 15000 to 18000; an estimated sales number we could call successful, surely. At least in the eyes of the producer and the hidden photographers. Perhaps not so much for their unknowingly photographed subjects.