You need to append a filename to $thumbDir
when calling make_thumb()
or else you will try to store the created thumbnail with the same name as the thumbnail directory:
foreach ($_FILES['img']['name'] as $filename) {
$tmp = $_FILES['img']['tmp_name'][$count];
$temp = $imgsDIR.$filename;
move_uploaded_file($tmp, $temp);
// make sure you have a filename and not only an directory path
make_thumb($temp, $thumbDIR.'/'.$filename, 150);
$temp='';
$tmp='';
$count++;
}