ASP.net verification Code Picture generation sample

  Site Verification code is a very common technique. Let me now describe how the technology is implemented

The verification code is a picture. We need to write a section of <IMG>,SRC in the foreground code to point to a page (validateimage.aspx).   Code as follows: <script language= "JavaScript" >           function changeimg () {            $ ("#imgCheckNo"). attr ("src", "validateimage.aspx?r=" + getrandom (999));        }         function getrandom (n) {return Math.floor (math.random () * n + 1) } </script>   <div> <img id= "Imgcheckno" src= validateimage.aspx "style=" Border-color: #000000; Border-width:1px;border-style:solid ">  <span onclick=" changeimg (); > Can't see clearly? change a </span>  </div> <div>    <div class= "LABELCSS" > Verification Code:</div> <div> <asp:textbox id= "Tbxcheckno" runat= "Server" cssclass= "Tbxcss" ></asp:TextBox> </div> <div> <asp:button id= "btnsubmit" runat= "Server" text= "Register Now" onclick= "btnSubmit_Click"/> </div>       validateimage.aspx is used to produce captcha pictures andSave the code value of the CAPTCHA to a cookie. Code as follows:   Code as follows: public partial class ValidateImage:System.Web.UI.Page     {        Pro tected void Page_Load (object sender, EventArgs e)         {            This. Createcheckcodeimage (Rndnum ());        }          ///<summary> generate verification code        /// </summary>        ///<returns></returns>         Private Strin G Rndnum ()         {            int number;             Char code;             string checkcode = String.Empty;               System.Random Random = new Random ();               for (int i = 0; i < 4; i++)             {      &NBsp         number = random. Next ();                 if (number% 2 = 0)             &NB Sp       code = (char) (' 0 ' + (char) (number% 10));                 else                 &NBSP ;   Code = (char) (' A ' + (char) (number% 26);                 Checkcode + = code. ToString ();                         RESPONSE.COOKIES.ADD (new HttpCookie ( "Yzmcode", Checkcode));             return checkcode;        }          ///<summary> page generation verification Code gif picture       &NB Sp </summary>        ///<param name= "Checkcode" ></param>       &NB Sp private void Createcheckcodeimage (string Checkcode)         {            if (Checkcode = null | | checkcode. Trim () = = String.Empty)                 return;             SYSTEM.DRAWING.BITMAP image = new System.Drawing.Bitmap (int) math.ceiling ( Checkcode.length * 12.5)), 22);             Graphics g = graphics.fromimage (image);             try             {        &NBS P      //Generate random generators                 Random Random = new Random ();                //Clear picture background color                 G.clear (Color.White);                //Picture background noise lines               &NBSP ; for (int i = 0; i < i++)     &NBSp           {                    INT x1 = Random . Next (image. Width);                     int x2 = random. Next (image. Width);                     int y1 = random. Next (image. Height);                     int y2 = random. Next (image. Height);                     G.drawline (new Pen (color.silver), x1, y1, x2, y2);                                   F ont font = new System.Drawing.Font (Arial), (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));                 System.Drawing.Drawing2D.LinearGradientBrush brush = new System.dr Awing. Drawing2d.lineargradientbrush (New Rectangle (0, 0,Image. Width, image. Height), Color.Blue, color.darkred, 1.2f, true);                 g.drawstring (checkcode, Font, brush, 2, 2);                //Picture foreground noise point               &NBSP ; for (int i = 0; i < i++)                 {        &NB Sp           int x = random. Next (image. Width);                     int y = random. Next (image. Height);                     image. SetPixel (x, Y, Color.FromArgb) (random. Next ()));                                /Picture border Line                 G.drawrectangle (new Pen (Color.silver), 0, 0, image. Width-1, image. HEIGHT-1);       &NBSp         System.IO.MemoryStream ms = new System.IO.MemoryStream ();                 image. Save (MS, SYSTEM.DRAWING.IMAGING.IMAGEFORMAT.GIF);                 response.clearcontent ();                 Response.ContentType = "Image/gif";                 Response.BinaryWrite (Ms. ToArray ());                         finally             {                G.dispose ()     &N       Bsp     image. Dispose ();                     {     }       finally Background event to determine if the current verification code is correct. The code is as follows: The     code is as follows: #region page control event         protected void btnSubmit_Click (object sender, EventArgs e)         {            String.Compare (request.cookies[) Yzmcode "]. Value, Tbxcheckno.text, True)!= 0             {                Response.Write ("<script>alert (' captcha error! ') </script> ");                         else         &NB Sp   {             //Response.Write ("<script>alert Verify right!!! ') </script> ");                       #endregion