目的，实现生成验证码的图片

private void CreateImage(string checkCode)
{
    int iwidth = (int)(checkCode.Length * 11.5);
    System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20);
    Graphics g = Graphics.FromImage(image);
    Font f = new System.Drawing.Font("Arial", 10, System.Drawing.FontStyle.Bold);
    Brush b = new System.Drawing.SolidBrush(Color.White);
    //g.FillRectangle(new System.Drawing.SolidBrush(Color.Blue),0,0,image.Width, image.Height);
    g.Clear(Color.Blue);
    g.DrawString(checkCode, f, b, 3, 3);
    // 添加横线
    Pen blackPen = new Pen(Color.Black, 0);
    Random rand = new Random();
    for (int i=0;i<5;i++)
    {
        int y = rand.Next(image.Height);
        g.DrawLine(blackPen,0,y,image.Width,y);
    }
   
    System.IO.MemoryStream ms = new System.IO.MemoryStream();
    image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);
    Response.ClearContent();
    Response.ContentType = "image/Jpeg";
    Response.BinaryWrite(ms.ToArray());
    g.Dispose();
    image.Dispose();
}

注释：本文摘抄自：为了明天，url:http://zt.cnblogs.com/page/42223/