java - How to add an image to a JFrame container?

i have this code where the container displays a specific background color.
Instead of displaying the color i want to add an image to the background,how should i do it?

public class mark {


public static void main(String[] args) {
    // TODO Auto-generated method stub

    wmmain m=new mark().new wmmain();
    m.setSize(800,500);
    m.setVisible(true); 

}
class wmmain extends JFrame /* MAIN WINDOW */

{
    Container container;

    public wmmain()
    {
        super("Digital Image WaterMarking");

        addWindowListener(new WindowAdapter()
        {
            public void windowClosing(WindowEvent e)

            {
                System.out.print("Exit");
                System.exit(0);
            }
        });



        container=this.getContentPane();
        container.setLayout(new BorderLayout());

        container.setBackground(new Color(72, 118, 255));

    }
    }
}