In this post i am going to show how to work with Arithmetic CAPTCHA. Generally we used , Alpha or alphaNumeric Captcha on most of the site but some site like ASP.SNIPPETS it shows ARITHMETIC CAPTCHA like 18 + 12 = ? so user have to give correct value then only it proceeds.
Here I am getting help from this site
http://www.knowlegezone.com/documents/80/Simple-ASPNET-CAPTCHA-Tutorial/
Which was in VB.NET so I would like to Written in C#, here I have been posted , On the Above link they used normal ASPX image to Generate the Image ie: 18 + 12 = .
So i written the code on Generic Handler File to improve the site performance.
By default Handler file does not Read or write the value to Session so we have to use like this
using System.Web.SessionState;
public class Captcha : IHttpHandler, IRequiresSessionState
suppose if we are going to read the Session value on HTTP Handler file
using System.Web.SessionState;
public class Captcha : IHttpHandler, IReadOnlySessionState
This is the full code for
Captcha.ashx file
<%@ WebHandler Language="C#" Class="Captcha" %>
using System;
using System.Web;
using System.Drawing;
using System.Web.SessionState;
public class Captcha : IHttpHandler, IRequiresSessionState
{
public void ProcessRequest (HttpContext context) {
//context.Response.ContentType = "text/plain";
//context.Response.Write("Hello World");
Random num1 = new Random();
Random num2 = new Random();
int numQ1 = 0;
int numQ2 = 0;
string QString = null;
numQ1 = num1.Next(10, 15);
numQ2 = num1.Next(17, 31);
QString = numQ1.ToString() + " + " + numQ2.ToString() + " = ";
int tAnswer = numQ1 + numQ2;
context.Session["answer"] = tAnswer .ToString ();
Bitmap bitmap = new Bitmap(85, 25);
Graphics Grfx = Graphics.FromImage(bitmap);
Font font = new Font("Arial", 18, FontStyle.Bold, GraphicsUnit.Pixel);
Rectangle Rect = new Rectangle(0, 0, 100, 25);
Grfx.FillRectangle(Brushes.Snow, Rect);
Grfx.DrawRectangle(Pens.White, Rect);
// Border
Grfx.DrawString(QString, font, Brushes.Black, 0, 0);
context.Response.ContentType = "Image/jpeg";
bitmap.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
bitmap.Dispose();
Grfx.Dispose();
}
public bool IsReusable {
get {
return false;
}
}
}
Here is the code if you are going to write it on
Captcha.aspx page
Explanation was given on Comment itself. Write the below code on
Page_Load Event
// Getting Random number
Random num1 = new Random();
Random num2 = new Random();
int numQ1 = 0;
int numQ2 = 0;
string QString = null;
// here we get the random number for the first and second numer - ie: shows the number in between the range.
numQ1 = num1.Next(10, 15);
numQ2 = num1.Next(17, 31);
//Total answer has been stored it on String and assign to the Session["number"]
QString = numQ1.ToString() + " + " + numQ2.ToString() + " = ";
Session["answer"] = numQ1 + numQ2;
// Here we create Bitmap width - 85 and height - 25
Bitmap bitmap = new Bitmap(85, 25);
Graphics Grfx = Graphics.FromImage(bitmap);
// Setting the font name, size etc for the text that we have to write it on the image
Font font = new Font("Arial", 18, FontStyle.Bold, GraphicsUnit.Pixel);
// Here we specify a Rectangle object of x , y co-ordinate , with width and height
Rectangle Rect = new Rectangle(0, 0, 100, 25);
//Fill the color to the Rectangle
Grfx.FillRectangle(Brushes.Snow ,Rect);
// Now Using Pen Object Drawing a rectangle
Grfx.DrawRectangle(Pens.White, Rect);
// Border - here drawing the string of the num1 and num 2, font size , type etc, font color , and x and y co-ordinate
Grfx.DrawString(QString, font, Brushes.Black , 0, 0);
// Specify the Content type of the image - here i am using JPEG
Response.ContentType = "Image/jpeg";
// Save the image and show it on page using response object
bitmap.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
//Dispose the object and release the resources
bitmap.Dispose();
Grfx.Dispose();
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