Well, by God you've done it - this is my night.

To touch off on one of your questions, my father's childhood (Early 50's) is very sparsely photographed compared to me and my siblings' childhood throughout the early 80s and 90s. This was due in part to photographers keeping the negatives in the studio, and you ordering the photographs for print directly from the photographer after sending in the negatives for development (If you had taken them), and also due to my family struggling financially until the late 60s.

There were rolls of film, of course, as film was developed late in the 19th century, but the photographers usually kept these on hand for further development and printing later on (As I said above). In regards to who took the photographs, that really depended on whether or not you had your own camera at home, or if you went to a photographic studio. From rooting through my father's photographs of him in an early age, there's a seeming lack of photographs in that department, too. I haven't actually seen any of my grandfather as a child yet for instance, but I haven't had a chance to root through the sheer mass of images we inherited from my late grandmothers house, but we have several hundreds (If not thousands) of card-mounted photographs of the late 19th century of all my relatives. There's him in his early teens, him as an Officer in the Army, and then him as a middle-aged man with my father and uncle. They weren't exceedingly wealthy, so this is a good explanation at least for that part.

Development, at least in the color department (My main forte), was quite laborious pre-1950. It was a mess of chemicals, and a very intricate and complicated method that really wasn't readily available to the layman, unless he had practiced it for a while. In 1938, Kodachrome and Agfacolor both came out with a new process capable of producing still color photography cheap and simply (To some extent)! It didn't require the usual fuss, you just photographed your intended subject and sent the film back to the manufacturer for processing, which involved the usual development, re-exposure, dyeing, and bleaching of the three coatings on the film.

In 1950, Leopold Godowsky Jr. and Leopold Mannes (Who were the inventors of Kodachrome) invented the Ektachrome (And later the Ektacolor process), which ranged in development time from an hour to about a day in an amateur studio, whereas the Kodachrome (With superior quality and color) would take several days to develop in a dedicated lab. This meant that you could now shoot (and develop) color photography a lot simpler than with the other processes, and amateur photographers could develop their own color photographs on their own terms without having to ship off their film for lengthy processing.

Professional photographs from WWII was mostly shot by the U.S. Signal Corps, and these would be a large format shot, as opposed to the 35mm cameras most soldiers carried. Soldiers of the German Wehrmacht were actually encouraged to carry cameras and photograph whatever they saw fit to strengthen the bond between the front line and the public. The Wehrmacht would develop a lot of their photographs for propaganda purposes, so they'd be shipped back to the manufacturers (Which meant a much superior quality to the private collections), while the more grizzly photographs taken by German soldiers would be dearly kept hidden until such a time that developing them wasn't a dangerous endeavor. Some photographs were supposedly snatched out of the pockets of dead Germans by the Russians and used as evidence of the cruelties visited by the Germans upon the Jewish populace. But, every-day soldiers would usually develop their photographs much like any other photographers, by sending them to the manufacturer of the film.

I can't comment on whether or not cameras were common, or more so in the German, Russian, or American army as the numbers of enlisted men varied wildly, but I can tell you that Germany kept a tight lid on a lot of the photographs that the men took. Himmler had strictly forbidden any photographs that showed the cruelty of war, the extermination of the Jews, or the executions of various resistance forces, among others.

Here's Soviet photographer, Natalia Bode, snapping a photograph with a 35mm camera, I always liked the photographs of photographers photographing (We must go deeper), it's very personal and really lends quite a nice touch to the image.

Anyway, to answer your last question, I haven't ever thought to look in to the sheer amount of cameras by enlisted men during the war, so I hope someone else here can chime in with that, if possible at all. It's not something I've ever studied or even looked in to, and none of my source material deals with the actual number of cameras, just the photographers themselves, so I'm a bit stumped here. I'll look around and see what I can find for you.

In any case, if you have further questions, by God feel free to ask them! Or if you'd like to elaborate and follow up some questions, by all means do so too. :)