WindowsFormApp（C#）でコントロールの上に手書きしたい

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Reflection;
using System.Windows.Forms;

public partial class Form1 : Form
{
    private Bitmap _Image;
    private bool _Drawing;

    public Form1()
    {
        InitializeComponent();

        _Image = new Bitmap(panel1.ClientSize.Width, panel1.ClientSize.Height, PixelFormat.Format32bppArgb);
        panel1.BackgroundImage = _Image;
        panel1.BackgroundImageLayout = ImageLayout.None;
        panel1.GetType().InvokeMember(
           "DoubleBuffered",
           BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.SetProperty,
           null,
           panel1,
           new object[] { true });

        using (var g = Graphics.FromImage(_Image))
        {
            g.Clear(Color.LightCyan);
        }

        SetMouseEvent(panel1);
        SetMouseEvent(label1);
    }

    private void SetMouseEvent(Control ctl)
    {
        ctl.MouseDown += Control_MouseDown;
        ctl.MouseMove += Control_MouseMove;
        ctl.MouseUp += Control_MouseUp;
    }

    private void PaintPanel()
    {
        if (!_Drawing)
            return;

        var posScreen = Control.MousePosition;
        var pos = panel1.PointToClient(posScreen);

        using (var g = Graphics.FromImage(_Image))
        {
            g.FillEllipse(Brushes.Black, pos.X - 5, pos.Y - 5, 10, 10);
        }
        panel1.Invalidate();
    }

    private void Control_MouseDown(object sender, MouseEventArgs e)
    {
        _Drawing = true;
        PaintPanel();
    }

    private void Control_MouseMove(object sender, MouseEventArgs e)
    {
        PaintPanel();
    }

    private void Control_MouseUp(object sender, MouseEventArgs e)
    {
        _Drawing = false;
    }
}