Captcha ASP script - prevents automated form sumbissions

     The main idea of a Captcha test (completely automated public Turing test to tell computers and humans apart) is to prevent automated form submission.
     This project is a very short VB Script source code, which let's you generate gif, jpg or png images with text which most people can easily read and enter to a form field, but automated computer program cannot.

About this project

     Some weeks ago I had really need this simple test for ASP (and ASP.Net also), but I found only some very long codes with css or some script generating bmp images. I have decided to create some code with a public object, usually installed on hostings. One of them is a Chart object from Office web components.

     So I created a short include generating a "human testing" images and some form samples written in ASP. You can download them from motobit.com site. The code is free. Please include a next link on your pages if you use this include or samples:

This site is using
<a href="https://www.motobit.com/util/captcha/" 
  title="Captcha ASP image test against automated form 
  submission">Captcha for ASP</a>

Using this VBScript code and includes

     This project contains one ASP include, _captcha.asp and several samples. Please take a look at sample1 folder, form-session.asp sample.
     form-session.asp generates a random text (using RandomText function from _captcha.asp), which is stored to a session.

response.cookies("checktext") = RandomText(5)

and the source form in form-session.asp contains one more text field named imagecheck:

<input type="text" name="imagecheck" size="5" />

Generate-captcha.asp script creates a GIF image with the random text, using textToGIF function and BinaryWrite method.

<!--#INCLUDE FILE="_captcha.asp"-->
<%
  response.ContentType = "image/gif"
  response.binarywrite textToGIF(request.cookies("checktext"))
%>

form-session.asp accepts form dat then and checks validity of text written by client.

if len(request("imagecheck"))>0 and _
  ucase("" & request("imagecheck")) = ucase("" & request.cookies("checktext")) then 
    response.write "The form was accepted."
end if

     You can see more technical details on How it works page.

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