Salvaschermo

Scusate se sto alle prime armi:
Come posso utilizzare una immagine BufferedImage (Catturata con Robot().createScreenCapture) mettendola come sfondo (magari senza cornice) e senza doverla salvare da qualche parte nel computer?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.awt.AWTException;
import java.awt.Robot;
import java.awt.Rectangle;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.*;
import javax.imageio.ImageIO;
import java.awt.Graphics;
import java.awt.Image;

class MyPanel extends JPanel implements ActionListener {
private Timer timer;
private final int PAUSE = 50;
int j,r;
MyPanel() {
try {
} catch(Exception e) {}
timer = new Timer(PAUSE, this);
timer.start();
}

public void actionPerformed(ActionEvent ae) {

/*repaint();*/
}
public void paintComponent(Graphics g) {
setOpaque(false);
Image img = Toolkit.getDefaultToolkit().createImage("/home/paolo/Scrivania/screencapture.jpg");
try {
MediaTracker track = new MediaTracker(this);
track.addImage(img, 0);
track.waitForID(0);
} catch (InterruptedException e) {
e.printStackTrace();
}
g.drawImage(img, 0, 0, null);
for(j=0;j<200;j++)
{
r=(int)(Math.random()*Math.random()*100);
g.drawOval((int) (Math.random()*1440),(int) (Math.random()*900),r,r);
}
}
}


class AnimationExample extends JFrame {
private MyPanel panel;

AnimationExample() {
super("Esempio Animazione");

panel = new MyPanel();
add(panel);

setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}

public static void makeGUI() {
AnimationExample ae = new AnimationExample();
ae.setSize(1440, 900);
ae.setVisible(true);
}

public static void main(String[] args) throws AWTException, IOException {
// capture the whole screen
BufferedImage screencapture = new Robot().createScreenCapture(
new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()) );

// Save as JPEG
File file = new File("/home/paolo/Scrivania/screencapture.jpg");
ImageIO.write(screencapture, "jpg", file);
try {
SwingUtilities.invokeAndWait(new Runnable() {
public void run() {
makeGUI();
}
});
} catch(Exception e) {}
}
}