<script type="text/javascript">
function bildperzufallladen () {
var bilder=["bild.jpg", "noch_ein_bild.jpg", "anderes_bild.jpg", "letztes_bild.jpg", "standard.jpg"];
var zufall=Math.floor(Math.random() * bilder.length);
var wohin = document.getElementById("dasBild");
if (wohin) wohin.src = bilder[zufall];
}
window.onload=function () {
bildperzufallladen ();
}
</script>

<img src="standard.jpg" alt="ein zufälliges Bild" id="dasBild">

<?php 
function getFiles($dir)  
{ 
    static $files; 
     
    $allowed_file_extensions = array(); 
    $allowed_file_extensions[] = 'gif'; 
    $allowed_file_extensions[] = 'bmp'; 
    $allowed_file_extensions[] = 'jpg'; 
    $allowed_file_extensions[] = 'jpeg'; 
    $allowed_file_extensions[] = 'png'; 
     
     
    $len = strlen($dir); 
    if($dir{$len-1} == '/') 
        $dir = substr($dir, 0, $len-1); 
     
    if(!is_dir($dir)) 
        return false; 
         
    $open = @opendir($dir); 
     
    if(!$open)  
        return false; 
     
    while($file = readdir($open)) {         
        if($file == "." || $file == "..")     
            continue; 
         
        if(is_dir($dir.'/'.$file)) { 
            getFiles($dir.'/'.$file); 
        }     
             
        $e = explode('.', $file); 
        $ext = $e[ count($e)-1 ]; 
         
        if( is_file($dir.'/'.$file) && in_array($ext, $allowed_file_extensions) ) { 
            $files[] = $dir.'/'.$file; 
        } 
    } 
     
    return $files; 
} 


$files = getFiles('picz/slideshow'); 
$rand = mt_rand(0, count($files)-1); 

echo '<a href="galerie.php"><img  src="'. $files[ $rand ] .' " width="189" height="132" align="center" /></a>'; 
?>