implementation of CAPTCHA in asp.net

Introduction

In this article lets see how to implement CAPTCHA in asp.net application which we generally see when we login or signup in different websites.It is used to protect websites from hackers and spammers. Firstly,CAPTCHA is not a  word, its an abbreviation which stands for Completely Automated Public Turing Test to tell Computers and Humans Apart,lets start doing...

Implementing Captcha

public partial class captcha : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //create object of Bitmap Class and set its width and height.
        Bitmap bmp = new Bitmap(180,50);
        //Create Graphics object and assign bitmap object to graphics' object.
        Graphics gp = Graphics.FromImage(bmp);
        gp.Clear(Color .OrangeRed);
        Font ft = new Font("arial", 30, FontStyle.Regular);
        //genetating random 6 digit random number
        string str = getcapt();
        //take returned value from method into session
        Session.Add("str",str);
        gp.DrawString(str, ft, Brushes.White, 2, 2);
        Response.ContentType = "image/GIF";
        bmp.Save(Response.OutputStream, ImageFormat.Gif);
        bmp.Dispose();
        gp.Dispose();
        ft.Dispose();

    }
    public string getcapt()
    {
        //u can allowed any characters which u want 
        string allowedchars = "a,b,c,d,e,f,g,h,j,k,m,n,p,q,r,s,t,u,v,w,x,y,z,";
        allowedchars += "A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z,";
        allowedchars += "2,3,4,5,6,7,8,9";
        char[] sep ={ ',' };
        string[] arr = allowedchars.Split(sep);
        string passwordchars = "";
        string temp;
        //creates random combination of letters and nos.


        Random rmd = new Random();
        int i;
        for (i = 0; i <= 6; i++)
        {
            temp = arr[rmd.Next(0, arr.Length)];
            passwordchars += temp;
        }
        return passwordchars ;
    }

}

Conclusion

This looks simple but used in almost every website which gives preference to security of their websites it protects from machine to login behaving like a human.

njoy coding
ankit saxena
Ankitsrist