implementation of CAPTCHA in

Posted by in ASP.NET category on for Beginner level | Points: 250 | Views : 8872 red flag
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Firstly CAPTCHA is not a word, its an abbreviation which stands for Completely Automated Public Turing Test to tell Human and Animal Apart..

 Download source code for implementation of CAPTCHA in


In this article lets see how to implement CAPTCHA in 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

Add a new website in Visual Studio. In Default.aspx, add image control which is in HTML section of Toolbox, one textbox and one button control in it. Add one another web page in root directory with name Captcha.aspx and in its code separation page write the following code,
don't forget to add three namespaces mentioned below:

using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Design;

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
gp.DrawString(str, ft, Brushes.White, 2, 2);
Response.ContentType = "image/GIF";
bmp.Save(Response.OutputStream, ImageFormat.Gif);

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 ;

After this in image control of Default.aspx page include src="Captcha.aspx"
then run ur application


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

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About the Author

Full Name: ankit saxena
Member Level: Starter
Member Status: Member
Member Since: 11/16/2012 11:33:51 PM
Country: India
hello, i have done engineering from I.T. branch, recently got placed in endroit technologies mumbai as a trainee engineer its my first company ...i was java developer but during job my interest towards has emerged :)

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Comments or Responses

Posted by: Kundan64 on: 1/23/2013 | Points: 25
Good article.
Posted by: Ankitsrist on: 1/23/2013 | Points: 25
thanks Kundan64 sir your compliements are very precious for me...

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