upload a GIF image inside a folder

[ungovernable]

i have this basic upload script which will upload an image inside "images/" folder.

It is very simple, and works with only one file

the problem is that it will work only with JPEG files Sad If i try to upload with a GIF image, the result will be a black image

could anyone help me to make it work with gif files?

<form action="<?php echo $_server['php-self'];  ?>" method="post" enctype="multipart/form-data" id="something" class="uniForm">
<?php
include("bands.php");
?><br>
        <input name="new_image" id="new_image" size="30" type="file" class="fileUpload" />
<br>
        <button name="submit" type="submit" class="submitButton">AJOUTER L'IMAGE</button>
</form>
<?php
$band = $_POST['band'];
        if(isset($_POST['submit'])){
          if (isset ($_FILES['new_image'])){
              $imagenamz = $_FILES['new_image']['name'];
/* $numz = time();
$nums = date('dmy');
$num1 = "$nums" . $numz;
$band = $_POST['band'];
echo $band;
echo "<hr>";
$imagename = "$band" . $num1;
echo $imagename;
*/
echo "L'image a &#233;t&#233; ajout&#233; dans l'album photos de <b>$band</b><hr><br>";
$originalname = $_FILES['new_image']['name'];
$date = date('dmy');
$imagename = "$band" . "_" . $date . "_" . $originalname;
echo $imagename;

          $source = $_FILES['new_image']['tmp_name'];
          $target = "images/".$imagename;
          move_uploaded_file($source, $target);

          $imagepath = $imagename;
          $save = "images/" . $imagepath; //This is the new file you saving
          $file = "images/" . $imagepath; //This is the original file

          list($width, $height) = getimagesize($file) ; 

          $modwidth = 800; 

          $diff = $width / $modwidth;

          $modheight = $height / $diff; 
          $tn = imagecreatetruecolor($modwidth, $modheight) ; 
          $image = imagecreatefromjpeg($file) ; 
          imagecopyresampled($tn, $image, 0, 0, 0, 0, $modwidth, $modheight, $width, $height) ; 

          imagejpeg($tn, $save, 100) ; 

          $save = "images/sml_" . $imagepath; //This is the new file you saving
          $file = "images/" . $imagepath; //This is the original file

          list($width, $height) = getimagesize($file) ; 

          $modwidth = 150; 

          $diff = $width / $modwidth;

          $modheight = $height / $diff; 
          $tn = imagecreatetruecolor($modwidth, $modheight) ; 
          $image = imagecreatefromjpeg($file) ; 
          imagecopyresampled($tn, $image, 0, 0, 0, 0, $modwidth, $modheight, $width, $height) ; 

          imagejpeg($tn, $save, 100) ; 
        echo "<img src='images/".$imagepath."'><br>";  
        echo "Thumbnail: <img src='images/sml_".$imagepath."'>"; 

      }
    }
?>

[ungovernable]

i'm also having another problem: the script includes a function to resize the main image if it exceeds a certain width

i have set it to 800
$modwidth = 800;

if works fine but my problem is when the width is less than 800 : the image will be resized to 800px width anyway, thus enlarging it, and loosing quality with big nasty pixels instead of a fluid image