#
$input = array("image1.jpg",
#
               "image2.jpg",
#
               "image3.jpg",
#
               "image4.jpg",
#
               "image5.jpg");
#
$site = "http://somesite.com/images/";
#
$random = array_rand($input, 1);
#
echo '<img src="'.$site.$random.'">';; 

<?php
/*
By Matt Mullenweg > http://photomatt.net
Inspired by Dan Benjamin > http://hiveware.com/imagerotator.php
Latest version always at:
http://photomatt.net/scripts/randomimage
*/// Make this the relative path to the images, like "../img" or "random/images/".
// If the images are in the same directory, leave it blank.
$folder = '';

// Space seperated list of extensions, you probably won't have to change this.
$exts = 'jpg jpeg png gif';

$files = array(); $i = -1; // Initialize some variables
if ('' == $folder) $folder = './';

$handle = opendir($folder);
$exts = explode(' ', $exts);
while (false !== ($file = readdir($handle))) {
foreach($exts as $ext) { // for each extension check the extension
if (preg_match('/\.'.$ext.'$/i', $file, $test)) { // faster than ereg, case insensitive
$files[] = $file; // it’s good
++$i;
}
}
}
closedir($handle); // We’re not using it anymore
mt_srand((double)microtime()*1000000); // seed for PHP < 4.2
$rand = mt_rand(0, $i); // $i was incremented as we went along

header('Location: '.$folder.$files[$rand]); // Voila!
?>