Displays a random GIF image at an unchanging direct URL/URI using PHP

Random Image From Direct URL.php

<?php
function random_pic($dir = '/var/www/images') {
    $files = glob($dir . '/*.gif');
    if (!$files) return false;

    $file = array_rand($files);
    return $files[$file];
}

function outputImage( $filename ) {
    header("Content-Type: image/gif");
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Content-Length: ' . filesize($filename ));
    ob_clean();
    flush();
    readfile($filename );
    exit;
}

// Get a filename
$filename = random_pic();

// Check that a file was found
if (!$filename) {
    header('HTTP/1.1 404 Not Found');
    die();
}

// Output the image
outputImage( $filename );
?>