This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
You need to scale the image to cover the entire space available. Using a FlowLayout is not the way to go since a FlowLayout always uses the preferred size of the component. So you should probably be using a BorderLayout. You can then add your image to the Background Panel.