C#

public static Rectangle clientRectangle

private static void _ctrl_BackgroundImageChanged(object sender, EventArgs e)
{
   Control ctrl = ((Control)sender);
   ctrl.Invalidate(clientRectangle, true);
   ctrl.Update();
   ctrl.Refresh();  // supposedly calls both previous two statements
}

private Graphics m_objGraphics;

private void pb_white_board_MouseMove(object sender, MouseEventArgs e)
        {
            Rectangle rectEllipse = new Rectangle();

            if (e.Button != MouseButtons.Left) return;

            rectEllipse.X = e.X - 1;
            rectEllipse.Y = e.Y - 1;
            rectEllipse.Width = 3;
            rectEllipse.Height = 3;

            //pb_white_board.Update();

            m_objGraphics.DrawEllipse(System.Drawing.Pens.Black, rectEllipse);
            Brush blackBrush = Brushes.Black;
            m_objGraphics.FillEllipse(blackBrush, rectEllipse);
        }

private void btn_save_whiteboard_Click(object sender, EventArgs e)
        {
            Bitmap bitmap = new Bitmap(pb_white_board.Width, pb_white_board.Height);
            pb_white_board.DrawToBitmap(bitmap, new Rectangle(0, 0, pb_white_board.Width, pb_white_board.Height));
            m_objGraphics.Save("image1.jpg", System.Drawing.Imaging.ImageFormat.Jpeg);
        }