在winfom picturebox画图（作点）如何随图片一起保存

点出来的点无法随图片保存下来，求助大神啊
下面是代码
public Form1()
{
InitializeComponent();
m_lsPoints = new List();

    }

    private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
    {
        Graphics g = ((PictureBox)sender).CreateGraphics();
        g.FillEllipse(Brushes.Red, e.X, e.Y, 4, 4);
        Point pt = new Point(e.X, e.Y);
        m_lsPoints.Add(pt);
        g.Dispose();
        int x = e.X;
        int y = e.Y;
        richTextBox1.AppendText ("(" + x + "," + y + ")"+"\r\n");
    }
            private void button3_Click(object sender, EventArgs e)
    {
        #region 保存图片
        Bitmap bmp = new Bitmap(pictureBox1.Image, pictureBox1.Width, pictureBox1.Height);
        Graphics g = Graphics.FromImage(bmp);

        bmp.Save("d://1.bmp", System.Drawing.Imaging.ImageFormat.Bmp);
        #endregion
            }

记录下点集合，在
Graphics g = Graphics.FromImage(bmp);
后面根据记录的点，绘图，即把你pictureBox1_MouseDown绘图的代码放在下面

能在上面代码的基础上写个出来吗？

http://www.cnblogs.com/stg609/archive/2008/03/30/1129221.html