There were cinematographers working to record events during the First World War. While a tiny number were amateurs, most were appointed by various governments and given access to places, people and objects that were not freely available to the average guy with a camera. At the time though, cinematography and photography went hand in hand, and the operator had to choose his medium carefully.

You are right in that the cameras themselves were bulky, difficult to use, and hand cranked which accounts for the jerky, sped-up nature of old footage. And you are also right to suspect that actual combat footage from the First World War is staged, because it almost invariably is. Not just because the cameras were difficult to use, but because battlefields are an extremely dangerous place to be, in fact, if you're not in a trench or behind a well- placed artillery barrage you're well on your way to being dead. Not the place to be standing around cranking a box.

Battlefields are also hard to see in. Despite our vision of the endless mud of the Western Front, it was often dry and dusty. Clouds of dust and dirt were kicked up by artillery fire and could hang around to destroy visibility even before the smoke shells were fired. Again, this is not going to result in good cinematography. The rule of thumb is if your are looking at anything not more detailed than grainy grey figures beetling over slightly less grey ground at a huge distance (there is a small amount of this, and it's always hard to make out what's going on) it's faked.

The footage of Australians landing on Gallipoli is actually from a feature film called the Hero of the Dardanelles and was shot on Tamarama Beach during the war using recruits from Liverpool camp. The famous Battle of the Somme "over the top" shots were put together by official cinematographers Geoffrey Malins and John McDowell. They are fascinating pieces of footage in their own right given the proximity they had to events even as they were being filmed. While there was plenty in the Hero of the Dardanelles soldiers found to ridicule, the landing scenes generally weren't. Similarly, Malins,' work was generally found acceptable, which indicates there is a ring if truth to them that was enough for many a veteran.

This is specifically to do with scenes of combat though. There's a great deal of authentic footage of soldiers and nurses at war to work through. The conundrum of getting good footage of the fighting itself was one that remained unsolved, however. The reproductions were the best they could do.