Need help just inserting an image in a JPanel

I want to know the quickest easiest way to insert an image in a JPanel

Here is my code so far

 import java.awt.*;
   import java.awt.event.*;
   import javax.swing.*;
   import java.text.DecimalFormat;

//Panel containing components
    public class CalculatePanel extends JPanel{
   //1) Declare components to be used
      private JLabel inputLabel, resultLabel;
      private JTextField xvar;
      private int x; private double ans;
      private JButton calcButton;
   //2) Sets up the GUI
       public CalculatePanel(){

      //2a) Create two labels
         inputLabel = new JLabel ("Enter posotive value of x:");
         resultLabel = new JLabel ("Value of expression");
      //2b) Create text field
         xvar = new JTextField (10);

      //2c) Add action listener to the text field
         xvar.addActionListener (new TextFieldListener());

      //2d) Add components to the panel
         add (inputLabel);
         add (xvar);
         add (resultLabel);
      //2e) set buttons and listeners
         calcButton = new JButton("Calculate Expression");
         calcButton.addActionListener(new CalcButtonListener());

         setPreferredSize (new Dimension(300, 450));
         setBackground (Color.green);

         add(calcButton);
      }

   //3) Create the action listener for the text field
       private class TextFieldListener implements ActionListener {
      //--------------------------------------------------------
      // Performs the conversion when the enter key is pressed in the
text field
      //--------------------------------------------------------
          public void actionPerformed (ActionEvent event){

            String text = xvar.getText();
            x = Integer.parseInt (text);
            double ans = Math.sqrt (Math.abs(3 * (Math.pow((x), 5)) -
(12 * (Math.pow((x), 4))) - (9 * (Math.pow((x), 2))) + (2 *
x)));
            DecimalFormat df = new DecimalFormat ("0.###");
            String result = "Value of expression = " + df.format(ans);
            resultLabel.setText (result);

         }
      }
       private class CalcButtonListener implements ActionListener
      {
          public void actionPerformed (ActionEvent event)
         {
            String text = xvar.getText();
            x = Integer.parseInt (text);
            double ans = Math.sqrt (Math.abs(3 * (Math.pow((x), 5)) -
(12 * (Math.pow((x), 4))) - (9 * (Math.pow((x), 2))) + (2 * x)));
String result = "Value of expression = " + ans;
            DecimalFormat df = new DecimalFormat ("0.###");
            String result1 = "Value of expression = " +
df.format(ans);
            resultLabel.setText (result1);
         }
      }
   }