Crop area selection control(like photoshop's) in c# windows form

 private Point _pt;
 private Point _pt2;
private void picBoxImageProcessing_MouseDown(object sender, MouseEventArgs e)
{
    //// Starting point of the selection:
    //if (e.Button == MouseButtons.Left)
    //{
    //    _selecting = true;
    //    _selection = new Rectangle(new Point(e.X, e.Y), new Size());
    //}

    if (e.Button == MouseButtons.Left)
    {
        int ix = (int)(e.X / _zoom);
        int iy = (int)(e.Y / _zoom);

        //reset _pt2
        _pt2 = new Point(0, 0);
        _pt = new Point(ix, iy);

        // pictureBox1.Invalidate();
        picBoxImageProcessing.Invalidate();
    }
}

private void picBoxImageProcessing_MouseUp(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left && _selecting)
    {
        _selecting = false;
    }
}

private void picBoxImageProcessing_Paint(object sender, PaintEventArgs e)
{
    //if (_selecting)
    //{
    //    // Draw a rectangle displaying the current selection
    //    Pen pen = new Pen(Color.Red, 4);
    //    e.Graphics.DrawRectangle(pen, _selection);
    //}

    if (_selecting &&_pt.X >= 0 && _pt.Y >= 0 && _pt2.X >= 0 && _pt2.Y >= 0)
    {

        e.Graphics.DrawRectangle(pen, _pt.X * _zoom, _pt.Y * _zoom, (_pt2.X - _pt.X) * _zoom, (_pt2.Y - _pt.Y) * _zoom);
    }
}

private void picBoxImageProcessing_MouseMove(object sender, MouseEventArgs e)
{
    // Update the actual size of the selection:
    //if (_selecting)
    //{
    //    _selection.Width = e.X - _selection.X;
    //    _selection.Height = e.Y - _selection.Y;

    //    // Redraw the picturebox:
    //    picBoxImageProcessing.Refresh();
    //}

    if (e.Button == MouseButtons.Left)
    {
        _selecting = true;
        int ix = (int)(e.X / _zoom);
        int iy = (int)(e.Y / _zoom);

        _pt2 = new Point(ix, iy);

        //  pictureBox1.Invalidate();
        picBoxImageProcessing.Invalidate();
    }
}