Whereas the majority of Allied fighter aircraft installed and routinely used gun cameras to verify claim kills, it seems most Axis aircraft didn't. The Germans for instance, only sparingly used an externally mounted camera in a streamlined pod. The reasons it seems are manifold, not least of which was the scarcity of strategically important Silver from which to make the Silver Iodide. Then there is the fact that as a Blitzkrieg invasion force the Luftwaffe were often operating from hastily improvised airfields so there were manning issues and the general lack of proper photo processing facilities. It's not hard to understand how this situation was exploited my over-ambitious pilots and lead to grossly inflated kill claims. The Japanese are a bit of a mystery, not sure how routinely they used gun camera's but certainly, not it appears, a standard installation. Personally, I've always been sceptical about the value of gun cameras - what about night-fighters for instance??
No agenda here, just opening up what may prove to be an interesting technical discussion. Vent your spleen!