[TonyWilliams]

No pics I'm afraid, but the following extract from Flying Guns – World War 1: Development of Aircraft Guns, Ammunition and Installations 1914-32 provides some background information:

It occurred to some designers that if the firing of machine guns needed to be physically linked to the propeller, it would be a logical progression, and in principle much simpler, to use engine power to drive the gun. The rate of fire would be directly linked to the engine and thereby the propeller speed, with none of the firing irregularities which accompanied synchronised systems. The most advanced design was developed in Austro-Hungary; the Gebauer, a twin-barrelled weapon which was successfully tested (on Aviatik D.I, D.II and D.III) and ordered in quantity, but appears to have been just too late to be used in the First World War, although a D.I armed with a Gebauer is claimed to have seen service with the Hungarian Red Airborne Corps postwar. The Gebauer weighed 21 kg and could fire at up to 1,600 rpm. After the war, the Allies destroyed the manufacturing facility but Ferencz Gebauer re-created and developed his design which went on to see service in two versions with the Hungarian Air Force in the Second World War.

Engine-driven designs were also produced by several German companies, namely Autogen, Fokker, Siemens-Schuckert and Wollerman; the Infantry Construction Bureau and the Aircraft Machine Gun Detachment at Döberitz also became involved. Fokker's design (which may actually have been by Lübbe) was also continued and patented postwar but not taken further. Another Fokker development was a 12-barrel rotary gun, also externally powered, of which no details except a photograph survive. The Siemens-Schuckert weapon was sufficiently advanced in development to be installed in a Fokker D.VII, although the results of this experiment are not known.

Tony Williams: Military gun and ammunition website and discussion forum