Accessing Webcam when implementing webcam security

I have implementing a program using java-Swing. That is a webcam based security tool. On active mode when image/position is changed, it gives a beep alarm.

But problem in that is,- its unable to access my web cam. I have already checked my webcam driver and its runs perfectly. But this program can't access webcam. I have already added jmf.jar.

package jcam;

import com.sun.media.util.BufferToBufferedImage;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.util.Vector;
import javax.media.Buffer;
import javax.media.CaptureDeviceInfo;
import javax.media.CaptureDeviceManager;
import javax.media.Manager;
import javax.media.MediaLocator;
import javax.media.Player;
import javax.media.control.FrameGrabbingControl;
import javax.media.format.VideoFormat;
import javax.media.util.BufferToImage;
import javax.swing.JFrame;
import jmapps.jmstudio.CaptureControlsDialog;

public class Jcam extends JFrame{

Player p;
Buffer buf;
BufferToImage btoi;
Image img, cimg;
boolean flag=false;
public Jcam(){
    super("Jcam");
    try {
    Vector v = CaptureDeviceManager.getDeviceList(null);
    CaptureDeviceInfo cam=null;
    for(int i=0; i<v.size(); i++){
        CaptureDeviceInfo dev = (CaptureDeviceInfo) v.elementAt(i);
        if(dev.getName().startsWith("vfw"))
        {
            cam=dev;
            break;
        }
        System.out.println(dev.getName());
    }
    if(cam==null)
    {
        System.out.println("no cam");
        System.exit(0);
      }
    MediaLocator locator = cam.getLocator();
    p = Manager.createRealizedPlayer(locator);
        add(p.getVisualComponent());
        p.start();
        Thread thread = new Thread(){
            public void run(){
                while (true) {                        
                    FrameGrabbingControl fgc = (FrameGrabbingControl)     
p.getControl("javax.media.control.FrameGrabbingControl");
                    buf= fgc.grabFrame();
                    btoi= new BufferToImage((VideoFormat) buf.getFormat());
                    cimg = btoi.createImage(buf);
                    if(img!=null){
                        if(com()>5999)
                            flag=true;
                    }
                    repaint();
                    img=cimg;
                }
            }
        };
    } catch (Exception e) {
        System.out.println(e);
    }
    setSize(700,700);
    setVisible(true);
}

public int com(){
    BufferedImage image1= (BufferedImage) cimg;
    BufferedImage image2= (BufferedImage) img;
    int H= image1.getHeight();
    int W= image1.getWidth();
    int c=0;
    for(int i=0; i<W;i++){
    for(int j=0; j<H; j++){
        int rgb = image1.getRGB(i, j);
        int rgb2 = image2.getRGB(i, j);

        int r1, r2, g1, g2, b1, b2;
        r1= (rgb & 0x00ff0000) >> 16;
        g1= (rgb & 0x0000ff00) >> 8;
        b1= (rgb & 0x000000ff);

        r2= (rgb2 & 0x00ff0000) >> 16;
        g2= (rgb2 & 0x0000ff00) >> 8;
        b2= (rgb2 & 0x000000ff);

        int red = r1-r2;
        int green = g1-g2;
        int blue = b1-b2;
        if(Math.abs(red)>30 || Math.abs(green)>30)
            c++;
    }
}
      return c;
}

public void paint(Graphics g){
    super.paint(g);
    if(flag){
        g.fillOval(300, 600, 50, 50);
        flag=false;
    }
}
public static void main(String[] args) {
    // TODO code application logic here
    new Jcam();
}

}

First: you should refactor your code and seperate Swing initialization from image capturing. Your Jcam constructor is bad style.

Second: here you define a thread

Thread thread = new Thread(){

but where it is started ?

Third: you should read about Swing threading: http://docs.oracle.com/javase/tutorial/uiswing/concurrency/