Captcha Implementaion using awt and javax image APIs

This is a code snippet which can be used to generate random captcha images. This implementation is a change password scenario where in the user has to enter the captcha in order to validate the change of password is being done by a person. Here is a Java Program to

import java.io.*;

import java.awt.*;

import java.awt.image.BufferedImage;

import java.net.*;

import java.util.Random;
import javax.imageio.ImageIO;


/**
 * Servlet implementation class CaptchaServlet
 */
public class Captcha {
 
  public Captcha() {
  super();
  // TODO Auto-generated constructor stub
 }

 public void generateCaptcha() 
 throws  IOException 
 {

  int width = 150;
  int height = 50;

  Random r=new Random();
  String token=Long.toString(Math.abs(r.nextLong()),36);
  String captcha=token.substring(0,6);

  BufferedImage bufferedImage = new BufferedImage(width, height, 
    BufferedImage.TYPE_INT_RGB);

  Graphics2D g2d = bufferedImage.createGraphics();

  Font font = new Font("Georgia", Font.BOLD, 18);
  g2d.setFont(font);

  RenderingHints rh = new RenderingHints(
    RenderingHints.KEY_ANTIALIASING,
    RenderingHints.VALUE_ANTIALIAS_ON);

  rh.put(RenderingHints.KEY_RENDERING, 
    RenderingHints.VALUE_RENDER_QUALITY);

  g2d.setRenderingHints(rh);

  GradientPaint gp = new GradientPaint(0, 0, 
    Color.red, 0, height/2, Color.black, true);

  g2d.setPaint(gp);
  g2d.fillRect(0, 0, width, height);

  g2d.setColor(new Color(255, 153, 0));
  int x = 0; 
  int y = 0;

  char[] arr=captcha.toCharArray();
  for (int i=0; i<6; i++) {
   x += 10 + (Math.abs(r.nextInt()) % 15);
   y = 20 + Math.abs(r.nextInt()) % 20;
   g2d.drawChars(arr, i, 1, x, y);
  }

  g2d.dispose();
//bufferedImage is the captcha image
   }