Du skulle kunna göra något sånt här:
if(isset($_FILES['userfile']))
{
$userfile_name = str_replace(" ","_",$_FILES['userfile']['name']);
$userfile_tmp = str_replace(" ","_",$_FILES['userfile']['tmp_name']);
$userfile_size = $_FILES['userfile']['size'];
$userfile_type = $_FILES['userfile']['type'];
$userfile_thumb_name = str_replace(" ","_",$_FILES['userfile']['name']);
$userfile_thumb_tmp = str_replace(" ","_",$_FILES['userfile']['tmp_name']);
// mappen där filerna ska hamna
$thumb_upload_dir = 'images/liten/';
$thumb_upload_dir2 = 'images/stor/';
// de tillåtna fil-typerna
/*****START EDIT**************/
$allow_images = array("image/gif", "image/jpeg", "image/png", "image/pjpeg", "image/jpg");
/*****END EDIT**************/
// den största tillåtna storleken ( 1000 kB )
$maxsize = (1024*20000);
// kolla om en fil har blivit angedd
if(empty($_FILES['userfile']['name']))
die("Du måste ange en bild som du vill ladda upp.<br />");
// kolla storleken på filen
if($_FILES['userfile']['size'] > $maxsize)
die("Tillåten filstorleken är '.round($maxsize / 1024).' kB.<br />");
// hämta filtypen
/*****START EDIT**************/
$filename_micro = microtime(true);
$filenameexplode = explode(".", $filename_micro);
$randomnumber = rand(100,999);
$filename_micro = $filenameexplode[0].$randomnumber;
$extension = strtolower( substr($_FILES['userfile']['name'], strrpos($_FILES['userfile']['name'], ".")) );
$_FILES['userfile']['name'] = $filename_micro.$extension;
/*****END EDIT**************/
// kolla filtypen
/*****START EDIT**************/
if(!in_array($_FILES['userfile']['type'], $allow_images)) {
die("Ogiltigt filformat.<br />");
/*****END EDIT**************/
if (file_exists($thumb_upload_dir.$insandare1.str_replace(" ","_",$_FILES['userfile']['name'])))
die("En bild med samma namn finns redan.<br />");
$insandare1 = minhemsida."_";
// Gör första tumnageln
thumb_pic(str_replace(" ","_",$_FILES['userfile']['tmp_name']), $thumb_upload_dir.$insandare1.str_replace(" ","_",$_FILES['userfile']['name']), 80, 60);
// Gör andra tumnageln
thumb_pic(str_replace(" ","_",$_FILES['userfile']['tmp_name']), $thumb_upload_dir2.$insandare1.str_replace(" ","_",$_FILES['userfile']['name']), 800, 600);
Ändrade även lite hur du kollar filtypen.

