Captcha Code In PHP

php and html Code 

<?php
//Random Number Generation
$rand=substr(rand(),0,4);//only show 4 numbers
?>
<form method="post" action="<?php $_SERVER['PHP_SELF']?>" name="form1">
<table>
<tr>
<td>Name:</td>
<td><input type="text" name="name">
<span id="name" class="color"></span>
</td>
</tr>
<tr>
<td>Enter Captcha</td>
<td><input type="text" name="chk" id="chk">
<span id="error" class="color"></span>
</td>
</tr>
<tr>
<td>&nbsp;</td>

<td><input type="text" value="<?=$rand?>" id="ran" readonly="readonly" class="captcha">
<input type="button" value="Referesh" onclick="captch()" /></td>
</tr>
<tr>
<td colspan="2">
<input type="submit" name="check" onclick="return validation();">
</td>
</table>
</form>






<?php
if(isset($_POST['check']))
{
echo "Form Submitted<br>";

echo "Name:".' '.$name=$_POST['name'];
}
?>

java script code

<script type="text/javascript">

//Javascript Captcha validation

function validation()

{

if(document.form1.name.value=="")

{

document.getElementById("name").innerHTML="Enter your Name!";

document.form1.name.focus();

return false;

}

if(document.form1.chk.value=="")

{

document.getElementById("error").innerHTML="Enter Captcha!";

document.form1.chk.focus();

return false;

}

if(document.form1.ran.value!=document.form1.chk.value)

{

document.getElementById("error").innerHTML="Captcha Not Matched!";

document.form1.chk.focus();

return false;

}

return true;

}

</script>

<script type="text/javascript">

//Javascript Referesh Random String

function captch() {

    var x = document.getElementById("ran")

    x.value = Math.floor((Math.random() * 10000) + 1);

}

</script>