above is a Belgian officer's cap, with the horsehide covering the helmet, and the long horsetail plume. Very flashy!
The horses were not used for cavalry tactics, but were put to use to carry shells. Thousands of horses died here of stupid things, like stepping on nails from blown apart boxes, and getting infections.
Above is a piece of trench art. These were often made by bored soldiers who were recuperating in field hospitals, as part of their physical therapy. The little tank is made from shell casings and the tracks are made from "drive bands" from exploded shells. The solder was melted out of the joints of tin cans, and the trail wheels are made from uniform buttons. Usually trench art is not quite so elaborate.