randomizing images

[AN-net]

it seems that my code will randomize if i run the the script through the browser but it doesnt randomize if i put it in an image page

<img src="$vboptions[bburl]/banners.php" />

and

the code is:

PHP Code:

<?php 
$img= array();
$img[] = "banner1.gif"; 
$img[] = "banner2.gif"; 
$img[] = "banner3.gif";
$img[] = "banner4.gif";
$img[] = "banner5.gif";
$img[] = "banner6.gif";
$img[] = "banner7.gif";
$img[] = "banner8.gif";
$img[] = "banner9.gif";
$dir = "http://dev.animationation.net/images/banners/";
$rand = rand(0, count($img) - 1); 
$img = $img["$rand"]; 
header("Location: $dir$img");
?>