public class CreateImage1 : IHttpHandler, IRequiresSessionState
{

    string[] FontItems = new string[] {   "Arial",
                                                      "Helvetica",
                                                      "Geneva",
                                                      "sans-serif",
                                                      "Verdana"
                                                  };

    Brush[] BrushItems = new Brush[] {     Brushes.OliveDrab,
                                                      Brushes.ForestGreen,
                                                      Brushes.DarkCyan,
                                                      Brushes.LightSlateGray,
                                                      Brushes.RoyalBlue,
                                                      Brushes.SlateBlue,
                                                      Brushes.DarkViolet,
                                                      Brushes.MediumVioletRed,
                                                      Brushes.IndianRed,
                                                      Brushes.Firebrick,
                                                      Brushes.Chocolate,
                                                      Brushes.Peru,
                                                      Brushes.Goldenrod
                                                };

    string[] BrushName = new string[] {    "OliveDrab",
                                                      "ForestGreen",
                                                      "DarkCyan",
                                                      "LightSlateGray",
                                                      "RoyalBlue",
                                                      "SlateBlue",
                                                      "DarkViolet",
                                                      "MediumVioletRed",
                                                      "IndianRed",
                                                      "Firebrick",
                                                      "Chocolate",
                                                      "Peru",
                                                      "Goldenrod"
                                                 };

    Color BackColor = Color.White;
    Pen BorderColor = Pens.DarkGray;
      int Width = 200;
      int Height = 60;
    Random r = new Random();
    int _brushNameIndex;
    public void ProcessRequest(HttpContext context)
    {
      
        context.Response.ContentType = "image/jpeg";
        Bitmap b = new Bitmap(200, 60);
        Graphics g = Graphics.FromImage(b);
        g.FillRectangle(new SolidBrush(Color.DarkGray), 0, 0, Width, Height);
        Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
        StringBuilder sb = new StringBuilder();
       
        //字符串集合 
        string letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890abcdefghijklmnopqrstuvwxyz";
        string letter;
       
        g.Clear(BackColor);//填充背景色
        for (int i = 0; i < 5; i++)
        {
            letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
            sb.Append(letter);
            g.DrawString(letter, GetFont(), GetBrush(), i * 38, r.Next(0, 15));
        }

        for (int n = 0; n < 30; n++)
        {
            int x = r.Next(200);
            int y = r.Next(60);
            b.SetPixel(x, y, Color.FromName(BrushName[_brushNameIndex]));
        }

        g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);
        //Pen linkPen = new Pen(new SolidBrush(Color.Black), 1);
        //for (int i = 0; i < 20; i++)
        //{
        //    g.DrawLine(linkPen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));

        //}
        b.Save(context.Response.OutputStream, ImageFormat.Jpeg);
        context.Session["validatecode"] = sb.ToString();

    }

    private Font GetFont()
    {
        int fontIndex = r.Next(0, FontItems.Length);
        FontStyle fontStyle = GetFontStyle(r.Next(0, 2));
        return new Font(FontItems[fontIndex], 24, fontStyle);
    }

 
   // 取一个字体的样式
    private FontStyle GetFontStyle(int index)
    {
        switch (index)
        {
            case 0:
                return FontStyle.Bold;
            case 1:
                return FontStyle.Italic;
            default:
                return FontStyle.Regular;
        }
    }

 
   // 随机取一个笔刷
    private Brush GetBrush()
    {
        int brushIndex = r.Next(0, BrushItems.Length);
        _brushNameIndex = brushIndex;
        return BrushItems[brushIndex];
    }

 
    // 绘画背景颜色
    private void Paint_Background(Graphics g)
    {
        g.Clear(BackColor);
    }

  
    // 绘画边框
    private void Paint_Border(Graphics g)
    {
        g.DrawRectangle(BorderColor, 0, 0, Width - 1, Height - 1);
    }

 
    public bool IsReusable
    {
        get
        {
            return false;
        }
    }
   

}

使用时，将IMAGE的SRC＝"createimage.ashx" 就可以了
效果图如下：