This image depicts the US dollar and Euros. Although they are both very strong world currencies, they both have unique differences.
The US Dollar is consider the world reserve currency. When a country wants to purchase oil on the world market, it must convert it's currency into dollars in order to complete the purchase. The paper currency commonly come in; 1, 2, 5, 10, 20, 50 and 100 dollar bills
The Euro is used by over 22 countries throughout Europe. It's typical Euro denominations are 5, 10, 20, 50, 100, 200 and 500.