Scritta al volo, prova così:

Codice PHP:
sendMail("../IMMAGINI/testata/", $_FILES, $_POST['nome'], 819200, 520, 200);

function sendMail($cartella, $files, $name, $maxSize, $resizeWidth, $resizeHeight) {
    include 'lib/wideimage/WideImage.php';
    $upload = FALSE;
    $acceptType = array('png' => 'image/png', 'jpeg' => 'image/jpeg', 'jpg' => 'image/jpg');
    for ($i = 0; $i < count($files['file']['name']); $i++) {
        if ($files['file']['name'][$i] != "") {
            list($width, $height, $type, $attr) = getimagesize($files['file']['tmp_name'][$i]);
            $nome_upload = $name . strrchr($files['file']['name'][$i], '.');
            $destinazione = $cartella . $nome_upload;
            if ($files['file']['size'][$i] <= $maxSize) {
                if (in_array($files['file']['type'][$i], $acceptType)) {
                    $image = WideImage::load($files['file']['tmp_name'][$i]);
                    $thumb = $image->resize($resizeWidth, $resizeHeight);
                    $thumb->saveToFile($destinazione);
                    $upload = TRUE;
                    if (!$upload) {
                        echo "Errore nell'upload
";
                    }
                } else {
                    echo "Tipo di file non valido
";
                }
            } else {
                echo "File troppo grande
";
            }
        }
    }
}