c#验证码

//image1.aspx.cs   图形验证码设计
protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            //  4位数字的验证码
            string str_ValidateCode = RndNum(4);
            //  用于验证的Session
            Session["ValidateCode"] = str_ValidateCode;
            CreateImage(str_ValidateCode);
        }
    }
    private string RndNum(int VcodeNum)
    {
        string Vchar = "0,1,2,3,4,5,6,7,8,9,a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p" +
         ",q,r,s,t,u,v,w,x,y,z";
        string[] VcArray = Vchar.Split(new Char[] { ',' });
        string VNum = "";
        //int temp = -1;
        Random rand = new Random();
        for (int i = 1; i < VcodeNum + 1; i++)
        {
            //if (temp != -1)
            //{
            //    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
            //}
            int t = rand.Next(36);
            //if (temp != -1 && temp == t)
            //{
            //    return RndNum(VcodeNum);
            //}
            //temp = t;
            VNum += VcArray[t];
        }
        return VNum;
    }
    //生成随机颜色

    private Color GetRandomColor()
    {
        Random RandomNum_First = new Random((int)DateTime.Now.Ticks);
        //  对于C#的随机数，没什么好说的
        System.Threading.Thread.Sleep(RandomNum_First.Next(50));
        Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks);       
      //  为了在白色背景上显示，尽量生成深色
      int int_Red = RandomNum_First.Next(256);
      int int_Green = RandomNum_Sencond.Next(256);
      int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green;
      int_Blue = (int_Blue > 255) ? 255 : int_Blue;
      return Color.FromArgb(int_Red, int_Green, int_Blue);
    }
    public void CreateImage(string str_ValidateCode)
    {
        int int_ImageWidth = str_ValidateCode.Length * 13;
        Random newRandom = new Random();
        //  图高20px
        Bitmap theBitmap = new Bitmap(int_ImageWidth, 20);
        Graphics theGraphics = Graphics.FromImage(theBitmap);
        //  白色背景
        theGraphics.Clear(Color.White);
        //  灰色边框
        theGraphics.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, int_ImageWidth - 1, 19);
        //  10pt的字体
        Font theFont = new Font("Arial", 10);
        for (int int_index = 0; int_index < str_ValidateCode.Length; int_index++)
        {
            string str_char = str_ValidateCode.Substring(int_index, 1);
            Brush newBrush = new SolidBrush(GetRandomColor());
            Point thePos = new Point(int_index * 13 + 1 + newRandom.Next(3), 1 + newRandom.Next(3));
            theGraphics.DrawString(str_char, theFont, newBrush, thePos);
        }
        //  将生成的图片发回客户端
        MemoryStream ms = new MemoryStream();
        theBitmap.Save(ms, ImageFormat.Jpeg );

        Response.ClearContent(); //需要输出图象信息 要修改HTTP头 
        Response.ContentType = "image/Png";
        Response.BinaryWrite(ms.ToArray());
        theGraphics.Dispose();
        theBitmap.Dispose();
        Response.End();
    }

image1.aspx什么都不用加

在需要验证码的页面上加入一个