C# 画像合成

[natori8808]

C#で画像の上に画像を表示させたいです（合成）
どうすればいいですか！？

コード:

using System;
using System.Windows.Forms;
using System.Drawing;

class Game1 : Form
{
    public static void Main()
    {
        Application.Run(new Game1());
    }
    public Game1()
    {
        this.Text = "Game";
        this.BackColor = Color.FromArgb(255, 255, 255);
        this.WindowState = FormWindowState.Maximized;

        this.Width = 1366;
        this.Height = 768;

        PictureBox start = new PictureBox();
        start.Image = Image.FromFile("d:\\start.png");
        start.Width = 338;
        start.Height = 149;
        start.Top = (this.Height - start.Height) / 2;
        start.Left = (this.Width - start.Width) / 2;

        start.Parent = this;

        start.Click += new EventHandler(start_Click);
    }
    public void start_Click(object sender, EventArgs e)
    {
        var start = sender as PictureBox;
        start.Visible = false;
        PictureBox stage1 = new PictureBox();
        stage1.Image = Image.FromFile("d:\\stage1.jpg");
        stage1.Width = 1920;
        stage1.Height = 1200;
        Graphics gr = stage1.CreateGraphics();
        PictureBox CharacterImg = new PictureBox();
        CharacterImg.Image = Image.FromFile("d:\\start.png");
        CharacterImg.Parent = this;
    }
}
 

[Math]

stage1.jpgとstart.pngを送ること。
Windowsの機能のみでコンパイル（PowerShell_ise使用）。
http://csi.nisinippon.com/z2.pngコンパイル
http://csi.nisinippon.com/z1.png実行結果
エラーはないけど論理的におかしい。全行にコメントをいれること。

コード:

    public void start_Click(object sender, EventArgs e)
    {
        var start = sender as PictureBox;
        start.Visible = false;
        PictureBox stage1 = new PictureBox();
        stage1.Image = Image.FromFile("d:\\stage1.jpg");
        stage1.Width = 1920;
        stage1.Height = 1200;
        Graphics gr = stage1.CreateGraphics();
        PictureBox CharacterImg = new PictureBox();
        CharacterImg.Image = Image.FromFile("d:\\start.png");
        CharacterImg.Parent = this;
    }

[natori8808]

ありがとうございます！！