This is maybe one of the most powerful pictures I have ever seen. The numbers on the arms are from prisoners of Nazi concentration camps. The numbers replaced their names while at the camps and they were tattooed on so that they could be easily tracked by the Germans. This is why we study history. So this never happens again.
October 1944: Oskar Schindler, a German officer, saves 1200 Jews by moving them from Plaszow labor camp to his factory in Sudetenland. Photograph shows Schindler (second from right) with a few of the Jewish workers he saved. Source: United States Holocaust Memorial Museum