Finding white rectangle in an image

This is very rough, but successfully finds all the white pixels in the image, more checking can be done to ensure it is the size you want and everything is there but the basics are there.

PS: I have not tested with your image. r and this.rc is picture size and p and this.px is the inner rectangle size

public static void main(String[] args) {
    JFrame frame = new JFrame();
    final int r = 100;
    final int p = 10;

    NewJPanel pan = new NewJPanel(r, p, new A() {
        @Override
        public void doImage(BufferedImage i) {
            int o = 0;

            for (int j = 0; j < i.getWidth() - p; j++) {
                for (int k = 0; k < i.getHeight() - p; k++) {

                    PixelGrabber pix2 = new PixelGrabber(
                            i, j, k, p, p, false);
                    try {
                        pix2.grabPixels();
                    } catch (InterruptedException ex) {}

                    int pixelColor = pix2.getColorModel()
                            .getRGB(pix2.getPixels());

                    Color c = new Color(pixelColor);
                    if (c.equals(Color.WHITE)) {
                        System.out.println("Found at : x:" + j + ",y:" + k);
                    }

                }
            }
        }
    });
frame.getContentPane().add(pan);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(500, 500);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

private interface A {
    void doImage(BufferedImage i);
}

private static class NewJPanel extends JPanel {
    private static final long serialVersionUID = -5348356640373105209L;

    private BufferedImage image = null;
    private int px;
    private int rc;
    private A a;

    public NewJPanel(int r, int p, A a) {
        this.px = p;
        this.rc = r;
        this.a = a;
    }

    public BufferedImage getImage() {
        return image;
    }

    @Override public void paint(Graphics g) {
        super.paint(g);

        image = new BufferedImage(this.rc, this.rc,
                BufferedImage.TYPE_INT_ARGB);
        java.awt.Graphics2D g2 = image.createGraphics();

        g2.setColor(Color.BLACK);
        g2.fillRect(0, 0, this.rc, this.rc);
        g2.setColor(Color.WHITE);
        g2.fillRect(
                new Random().nextInt(this.rc - this.px),
                new Random().nextInt(this.rc - this.px),
                this.px, this.px);

        g.drawImage(image, this.rc, this.rc, this);
        this.a.doImage(this.image);
    }
}

    frame.getContentPane().add(pan);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(500, 500);