rating system-is there a way to set up a unique voter ID

[benchviews]

Hi,

I'm trying to make a rating system, but I don't want people to vote more than once. Can I limit one vote per IP address for each specific ID?

here's my code.

<?php
ob_start();
include 'connect.php';
 $id = $_GET['id'];
// submit
if ($_POST['submit'])
{
	//get data
	$id_post = $_POST['id'];
	$rating_post = $_POST['rating'];

	if ($rating_post <=5&&$rating_post >0)
	{
 $get = mysql_query("SELECT * FROM photographs WHERE id='$id_post'");	
 $get = mysql_fetch_assoc($get);
 $get = $get['rating'];

 if ($get==0)
 	$newrating = $get + $rating_post;
 else
	$newrating = ($get + $rating_post)/2;

 $update = mysql_query("UPDATE photographs SET rating='$newrating' WHERE id='$id_post'");
		}
 header("Location: index.php");
}
?>
<form action="rate.php" method="POST">
Choose Rating:
<br>
<select name="rating">
<option>1</option>
<option>2</option>
<option>3</option>
<option>4</option>
<option>5</option>
</select>

<input type="hidden" name="id" value="<?php echo $id; ?>">
<input type="submit" name="submit" value="Rate!">
</form>