C# Web (Asp.net) อยากเพิ่มรูปไฟล์ .png บนรูปพื้นหลัง ทำอย่างไร

private void Page_Load(object sender, System.EventArgs e)
		{
			//Load the Image to be written on.
			
            Bitmap bitMapImage = new System.Drawing.Bitmap( Server.MapPath("dallen.jpg" )  );
			Graphics graphicImage = Graphics.FromImage( bitMapImage );

			//Smooth graphics is nice.
			graphicImage.SmoothingMode = SmoothingMode.AntiAlias;

			//I am drawing a oval around my text.
			graphicImage.DrawArc(new Pen(Color.Red, 3), 90, 235, 150, 50, 0, 360);

			//Write your text.
			graphicImage.DrawString( "That's my boy!", new Font("Arial", 12,FontStyle.Bold ), SystemBrushes.WindowText, new Point( 100, 250 ) );

			//Set the content type
			Response.ContentType="image/jpeg";

			//Save the new image to the response output stream.
			bitMapImage.Save(Response.OutputStream, ImageFormat.Jpeg);

			//Clean house.
			graphicImage.Dispose();
			bitMapImage.Dispose();   
		}