How can I display a BufferedImage in a JFrame?

You will have to repaint the JFrame whenever you update the image.

Here is what a simple google on the topic brings up: (I use those tutorials for all my Java coding)

Java Tutorial: Drawing an Image

To build on camickr's solution (for the lazy like me who want quick code to copy/paste) here's a code illustration:

JFrame frame = new JFrame();
frame.getContentPane().setLayout(new FlowLayout());
frame.getContentPane().add(new JLabel(new ImageIcon(img)));
frame.getContentPane().add(new JLabel(new ImageIcon(img2)));
frame.getContentPane().add(new JLabel(new ImageIcon(img3)));
frame.pack();
frame.setVisible(true);
//frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); // if you want the X button to close the app

Just incase life's to short too read the official docs here's a dirty way to get it done multiple times over

private static JFrame frame;
private static JLabel label;
public static void display(BufferedImage image){
   if(frame==null){
       frame=new JFrame();
       frame.setTitle("stained_image");
       frame.setSize(image.getWidth(), image.getHeight());
       frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
       label=new JLabel();
       label.setIcon(new ImageIcon(image));
       frame.getContentPane().add(label,BorderLayout.CENTER);
       frame.setLocationRelativeTo(null);
       frame.pack();
       frame.setVisible(true);
   }else label.setIcon(new ImageIcon(image));
}