Answer:
1: The picture and the disease mentioned (spanish influenza)
Why? Because this disease was first mentioned back in 1918 and lasted till 1920
2: Picture and the "coughs and sneezes spread diseases"" part because its directed that sneezing and coughing is the issue and you should cover those things up
3: "Coughs and sneezes" and "poison gas shells" showing that some simple coughs and sneezes can be the reason a multitude of people are dying. There for setting the purpose as to protect as many people from this sickness as possible
4: The point of view of the creator is that 1 coughing and sneezing are a central point of issue, and 2 that this sickness is extreamly dangerous and needs to be stopped. What tells me this is the picture dipicting a very ugly looking after affect of the possible disease. Aswell as the "As deadly as poison shells" Part because its dipicting that its extreamly deadly going along with his point futhure more.