请教大家这段代码哪里有问题啊？
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Text;
public partial class SuperUser_FreewayWheather : System.Web.UI.Page
{
  protected void Page_Load(object sender, EventArgs e)
  {
  GraphicsImage();
  }
  private void GraphicsImage()
  {
  Bitmap image = new Bitmap("11.jpg");
  try
  {
  Brush brush = new SolidBrush(Color.Red);
  Pen pen = new Pen(Color.Blue, 1);
  Graphics g = Graphics.FromImage(image);
  g.DrawLine(pen, 300, 150, 400, 150);
  System.IO.MemoryStream ms = new System.IO.MemoryStream();
  image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
  Response.ContentType = "image/Gif";
  Response.BinaryWrite(ms.ToArray());
  }
  catch (Exception ms)
  {
  Response.Write(ms.Message);
  }
  }
}


代码说明：我想用这段代码实现在一张底图（11.JPG）上绘制一段直线，我运行了以后总是在这句出错Bitmap image = new Bitmap("11.jpg");
请教大家哪里不对，谢谢！

------解决方案--------------------
1.
Bitmap B = new Bitmap(width, height);
B.SetPixel(x,y,Color.FromARGB(redvalue, greenvalue, bluevalue));

or 
2
using (Graphics G = Graphics.FromImage('11.jpg')) 
{
G.DrawLine(...);
G.FillElliipse(...);
// etc.
}