ti posto il codice per l'upload che uso io, devi cambiare le variabili penso

Codice PHP:
<?php
$upload_dir 
$_SERVER["DOCUMENT_ROOT"] . "/sky"// directory upload
$new_name "";
$file_name = ($new_name) ? $new_name $_FILES["upfile"]["name"];
if(
trim($_FILES["upfile"]["name"]) == ""
    {
        die(
"Non hai indicato il file da uploadare !");
    }
if(@
is_uploaded_file($_FILES["upfile"]["tmp_name"])) 
    {
        @
move_uploaded_file($_FILES["upfile"]["tmp_name"], "$upload_dir/$file_name"
        or die(
"Impossibile spostare il file, controlla l'esistenza o i permessi della directory dove fare         l'upload.");
    } 
else 
    {
        die(
"Problemi nell'upload del file " $_FILES["upfile"]["name"]);
    }
?>
comunque prima di cambiare script prova a modificare

$directory_upload= $_SERVER['DOCUMENT_ROOT']."/img_form/";

con

$directory_upload= $_SERVER['DOCUMENT_ROOT']."img_form/";