Most of the websites use the technique of captcha for validation / verification purpose whenever someone tries accomplish membership or want to submit a piece of information. The generation of captcha can be done in various ways. We can use server side scripting or even we can use client side scripting.
I am need to host SharePoint 2010 in shared environment and does not allow me to deploy server side control. Then tha best way to use captcha is javascript.
Here is a sample code of capatcha using javascript:
<html>
<head>
<title>Captcha</title>
<script type="text/javascript">
//Created / Generates the captcha function
function DrawCaptcha()
{
var a = Math.ceil(Math.random() * 10)+ '';
var b = Math.ceil(Math.random() * 10)+ '';
var c = Math.ceil(Math.random() * 10)+ '';
var d = Math.ceil(Math.random() * 10)+ '';
var e = Math.ceil(Math.random() * 10)+ '';
var f = Math.ceil(Math.random() * 10)+ '';
var g = Math.ceil(Math.random() * 10)+ '';
var code = a + ' ' + b + ' ' + ' ' + c + ' ' + d + ' ' + e + ' '+ f + ' ' + g;
document.getElementById("txtCaptcha").value = code
}
// Validate the Entered input aganist the generated security code function
function ValidCaptcha(){
var str1 = removeSpaces(document.getElementById('txtCaptcha').value);
var str2 = removeSpaces(document.getElementById('txtInput').value);
if (str1 == str2) return true;
return false;
}
// Remove the spaces from the entered and generated code
function removeSpaces(string)
{
return string.split(' ').join('');
}
</script>
</head>
<body onload="DrawCaptcha();">
<table>
<tr>
<td>
Welcome To Captcha<br />
</td>
</tr>
<tr>
<td>
<input type="text" id="txtCaptcha"
style="background-image:url(1.jpg); text-align:center; border:none;
font-weight:bold; font-family:Modern" />
<input type="button" id="btnrefresh" value="Refresh" onclick="DrawCaptcha();" />
</td>
</tr>
<tr>
<td>
<input type="text" id="txtInput"/>
</td>
</tr>
<tr>
<td>
<input id="Button1" type="button" value="Check" onclick="alert(ValidCaptcha());"/>
</td>
</tr>
</table>
</body>
</html>
This is simple but you can complicate it to eliminate cracking.
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