Draw rectangle on picturebox (moving with mouse)

[Red Head]

Hello

I've written some code to draw a rectangle on a picture box when the user moves the mouse.
(the previous rectangle is cleared)
This works fine but the very first rectangle is not removed from the screen.

here is my code

[PHP]
private Rectangle r = new Rectangle(new Point(0,0), new Size(0,0));

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
{
Point startPoint = ((Control)sender).PointToScreen(new Point(e.X, e.Y));


ControlPaint.DrawReversibleFrame(r, this.BackColor, FrameStyle.Dashed);

r = new Rectangle(startPoint.X, startPoint.Y, 100, 200);
ControlPaint.DrawReversibleFrame(r, this.BackColor, FrameStyle.Dashed);
}
[/PHP]