Compare two images....?

Suggestions on the best (preferably easiest way) to compare two images
(captured both from the desktop via java robot) ?

The following code is the code I will be using to take the screen shot
(currently it saves just to a file):

import java.awt.*;
import java.awt.image.*;
import java.io.*;
import javax.imageio.*;

class Screenshot{

static public void main()
{
 try
 {
  //Get the screen size
  Toolkit toolkit = Toolkit.getDefaultToolkit();
  Dimension screenSize = toolkit.getScreenSize();
  Rectangle rect = new
Rectangle(0,0,screenSize.width,screenSize.height);
  Robot robot = new Robot();
  BufferedImage image = robot.createScreenCapture(rect);
  File file;

  //Save the screenshot as a png
  file = new File("screen.png");
  ImageIO.write(image, "png", file);

  //Save the screenshot as a jpg
  file = new File("screen.jpg");
  ImageIO.write(image, "jpg", file);
 }
 catch (Exception e)
 {
  System.out.println(e.getMessage());
 }
}
}

Thank you,
Peter (thebigpj)