errori in conversione da gif/png a jpg

[gabar-el]

ciao, sto facendo prove in locale per caricare delle immagini, nello specifico per convertire l'estensione (qualunque) in jpg, ma riscontro svariati problemi. Se l'immagine è jpg tutto è ok, se si tratta di gif o png ricevo questi warning:

Warning: imagecopyresampled(): supplied argument is not a valid Image resource in C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\prova\capitolo7\check_image.php on line 44

Warning: imagedestroy(): supplied argument is not a valid Image resource in C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\prova\capitolo7\check_image.php on line 46

Warning: Cannot modify header information - headers already sent by (output started at C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\prova\capitolo7\check_image.php:44) in C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\prova\capitolo7\check_image.php on line 50

Warning: rename(C:/Programmi/Apache Software Foundation/Apache2.2/htdocs/prova/images/immagine.gif,C:/Programmi/Apache Software Foundation/Apache2.2/htdocs/prova/images/21.jpg) [function.rename]: File exists in C:\Programmi\Apache Software Foundation\Apache2.2\htdocs\prova\capitolo7\check_image.php on line 53

il che mi fa capire che il codice di conversione non si comporta correttamente, ma non riesco a decifrare bene i warning.
questo il codice:

$image_caption =$_POST['image_caption'];
$image_username = $_POST['image_username'];
$image_tempname = $_FILES['image_filename'] ['name'];
$today = date("Y-m-d");

$ImageDir ="C:/Programmi/Apache Software Foundation/Apache2.2/htdocs/prova/images/";
$ImageName = $ImageDir . $image_tempname;

if (move_uploaded_file($_FILES['image_filename']['tmp_name'],$ImageName)) {
    list($width, $height, $type, $attr) = getimagesize($ImageName);
    
if ($type > 3) {
    echo "Sorry, but the file you uploaded was not a GIF, JPG, or PNG file.
";
    echo "Please hit your browser's 'back' button and try again.";
} else {
        
        $insert = "INSERT INTO images
                    (image_caption, image_username, image_date)
                    VALUES
                    ('$image_caption', '$image_username', '$today')";
        $insertresults = mysql_query($insert)
            or die(mysql_error());
        
        $lastpicid = mysql_insert_id();
        
        $newfilename = $ImageDir . $lastpicid . ".jpg";
        
        if ($type == 2) {
            rename($ImageName, $newfilename);
        } else {
            if (type == 1) {
                $image_old = imagecreatefromgif($ImageName);
            } elseif ($type == 3) {
                $image_old = imagecreatefrompng($ImageName);
            }
            
            $image_jpg = imagecreatetruecolor($width, $height);
                imagecopyresampled($image_jpg, $image_old, 0, 0, 0, 0, $width, $height, $width, $height);
                imagejpeg($image_jpg, $newfilename);
                imagedestroy($image_old);
                imagedestroy($image_jpg);
            }
            $url = "location: showimage.php?id=" . $lastpicid;
            header($url);
        }
        
        rename($ImageName, $newfilename);
    } 

Inoltre in un'immagine jpg che ho caricato correttamente mi ritrovo lo sfondo nero che in partenza era bianco....

grazie