gistfile1.cs

using System;
using System.Drawing;

public class CSharpTest
{
	static void Main(string[] args)
	{
		Bitmap b = new Bitmap("a.jpg");
		Bitmap newImage = new Bitmap(b.Width, b.Height * 2, Graphics.FromImage(b));
		Graphics g = Graphics.FromImage(newImage);
		g.DrawImage(b, 0, 0);
		g.DrawImage(b, 0, b.Height);
		newImage.Save("hoge.jpg");
	}
}