ASP. NET Captcha Image Generation Example

The verification code is a picture. We need to write a paragraph in the foreground code <IMG>,SRC point to a page (validateimage.aspx).

<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> <span onclick=" changeimg (); " > not clear? change </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 images, and the code values of the verification code are saved to the cookie.
The code is as follows:

Public partial class ValidateImage:System.Web.UI.Page {protected void Page_Load (object sender, EventArgs e) {this.        Createcheckcodeimage (Rndnum ()); }///<summary> Generate verification Code///</summary>//<returns></returns> Private St            Ring Rndnum () {int number;            char code;            string checkcode = String.Empty;            System.Random random = new Random (); for (int i = 0; i < 4; i++) {number = random.                Next ();                if (number% 2 = = 0) code = (char) (' 0 ' + (char) (number% 10));                else Code = (char) (' A ' + (char) (number% 26)); Checkcode + = code.            ToString ();            } Response.Cookies.Add (New HttpCookie ("Yzmcode", Checkcode));        return checkcode; }///<summary> generate CAPTCHA GIF images to page///</summary>//<param name="Checkcode" ></param> 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 {//Generate random generator randomly random = new random ();                Empty the picture background color g.clear (color.white); Picture the background noise line for (int i = 0; i < i++) {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); } Font font = new System.Drawing.Font ("Arial", and (System.Drawing.FontStyle.bold |                System.Drawing.FontStyle.Italic)); System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.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 the foreground noise point for (int i = 0; i < i++) {int x = random. Next (image.                    Width); int y = random. Next (image.                    Height); Image. SetPixel (x, Y, Color.FromArgb (random.                Next ())); }//Draw the border line of the picture G.drawrectangle (new Pen (Color.silver), 0, 0, image. Width-1, image.                HEIGHT-1);                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 (); Image.            Dispose (); }        }    }

The last is the background event, to determine whether the current verification code is correct.
The code is as follows:

#region Page control event        protected void btnSubmit_Click (object sender, EventArgs e)        {            if (String.Compare ( request.cookies["Yzmcode"]. Value, Tbxcheckno.text, true)! = 0)            {                Response.Write ("<script>alert (' captcha is wrong! ') </script> ");            }            else            {               //Response.Write (' <script>alert (' verify correct!!! ') </script> ");            }        }  #endregion