title: Paint with brush on existing image
body: <p>I have embedded the code below in a project in which a want to paint with a brush OVER a picture. The problem is that if a write this code for a main panel , everything goes fine, but as I want to use it for an existing image, I can not see the brush. I suppose that the brush paints but it is a matter of foreground / background.</p>
  
  <pre><code>//the first line goes to the main form  - under the initialize component
  graphics = DisplayPicturebox.CreateGraphics();
  
  bool draw = false;
  Graphics graphics;
  
  private void DisplayPicturebox_MouseDown(object sender, MouseEventArgs e)
  {
      draw = true;
  }
  
  private void DisplayPicturebox_MouseUp(object sender, MouseEventArgs e)
  {
      draw = false;
  }
  
  private void DisplayPicturebox_MouseMove(object sender, MouseEventArgs e)
  {
      if (draw)
      {
          //create a brush:
          SolidBrush MysolidBrush = new SolidBrush(Color.Red);
          graphics.FillEllipse(MysolidBrush, e.X, e.Y,
                        Convert.ToInt32(toolStripTextBox1.Text),
                        Convert.ToInt32(toolStripTextBox1.Text));
      }
  }
  </code></pre>