Innovation happens on the margins of our world's knowledge and tools, in the place Steven Johnson has popularized as "the adjacent possible." We tend to focus on this space when looking at the major innovations, how so-and-so used existing technologies to make something fundamentally new. But out there at the margins of tech, lots of things get tried and have some success. Take Dr. Julius Neubronner's combination of three very different technologies: the homing pigeon, the newly miniaturized roll-film camera, and the timer.
The mechanisms were simple. A camera with a pneumatic timing mechanism was attached to a bird with a cute little harness. Then, the bird was released, and every so often, the timer would go off, and a puff of compressed air would trigger the exposure. The birds had a range of something like 60 miles, which meant they could get substantial coverage (albeit not if enemy lines were neatly drawn).
The heyday for carrier pigeon photography was definitely World War I, in which Neubronner brought his birds to the battles of Verdun and Somme. The Spy Museum in Washington, DC has a room dedicated to the surveillance service the birds rendered.