Your photo isn't good enough to really tell, but wrought iron has a grain. With very rusty wrought iron, sometimes times you can see the grain. If you pound on wrought iron cold, the grain will separate. Or, if you don't mind doing a grinding test, wrought iron makes an orange spark with no sparkles. Steel makes a brighter spark that sparkles. I don't know when they stopped using wrought iron and went totally to mild steel, but in the 1940's there were wrought iron nails and re-bar, which I know for a fact from personal experience.