Captcha implementation using Javascript

This tutorials shows a very simple way of developing captcha by using html and javascript code. You have to create some images with png extension that contains some characters without any order to test the following code.

Steps:

1. Create some images for using as captcha text.
2. Create a html file named captcha.html  and add the following script in the head section.


<script language="javascript">
var imgarray = ["GRYX","MDAO","PKHJ","FQUV","SKHW"];
var rimg = new Image();
var index;

function RandomImage()
{
index = Math.random();
index = Math.floor(index*10);
var l = imgarray.length-1;
if(index > l) index= index%l;
rimg.src = "Images/"+index+".png";
document.vimg.src= rimg.src;

}
function Check()
{
var val = document.v.t.value;
var match_t = false;
for(var i=0; i<imgarray.length; i++)
{
if(val == imgarray[i] && (i == index))
{
match_t = true;
break;
}
}
if(match_t == false)
alert("Invalid Entry");
else
alert("valid Entry");
}

function Check_key(e)
{
if (e.keyCode == 13) {
Check();

}

}

</script>

3. Add the following code with body tag.


<body onload="RandomImage()">
<div>
<form name="v">
<img name="vimg" /><br/>
<input type="text" name="t" onblur="Check()" />
</form>
</div>
</body>

4. Run the file from the browser.

You can visit the following video to clear the steps.