Sometimes a painting like this just tells the story for you.
We know that the night before Waterloo, the rains made the battlefield wet. I know that, in my story, the sorts of things that you see in this painting will be details that will make The Chasseurs react to what they find when they arrive. They will have spent days shadowing the armies, trying to avoid the confusion of calvary scouts and wayward units and deserters. They will find these rifles stacked everywhere and smell who owns them.
The way that dogs smell will mean a lot in this story. What a narrator or an all-knowing narrative might say can really be summed up by the fact that these dogs know what the Prussians, British, French and whoever else smelled like.
Storytelling tricks. You have to have them.