image upload and resize

i have a few questions...  below is my current code for resizing my images


my first question would be what would be the best size to use for a profile picture/avator ??  at the moment is have $modwidth = 200; but if i have a long picture then it looks too big..if you upload a picure nearly in all perportions then it looks great... is there anyway to make it more perpotionate or anything?

my second question would be how could i stop anything but images beeing uploaded?

3rd;y is there any more enhnace ments any 1 can suggest?

<?php
error_reporting(E_ALL); 
session_start();
require_once '../settings.php';
include "../info.php"; // sets username/id ect
?><form action="<?php echo $_server['php-self'];  ?>" method="post" enctype="multipart/form-data" id="something" class="uniForm">
        <input name="new_image" id="new_image" size="30" type="file" class="fileUpload" />
        <button name="submit" type="submit" class="submitButton">Upload/Resize Image</button>
</form>
<?php
        if(isset($_POST['submit'])){
          if (isset ($_FILES['new_image'])){
              			  $file_name = $_FILES['new_image']['name'];
			   	$getExt = explode ('.', $file_name);
               	$file_ext = $getExt[count($getExt)-1];
				$imagename = "$id.$file_ext";
				
              $source = $_FILES['new_image']['tmp_name'];
              $target = "images/$id.$file_ext";
			  
              move_uploaded_file($source, $target);
 
              $imagepath = $imagename;
              $save = "images/thumbs/" . $imagepath; //This is the new file you saving
              $file = "images/" . $imagepath; //This is the original file
 
              list($width, $height) = getimagesize($file) ; 
 
              $modwidth = 200; 
 
              $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) ; 
 
              $imagepath = $imagename;
              $save = "images/mini/" . $imagepath; //This is the new file you saving
              $file = "images/" . $imagepath; //This is the original file
 
              list($width, $height) = getimagesize($file) ; 
 
              $modwidth = 80; 
 
              $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) ; 
			  
			  
			  $imagepath = $imagename;
              $save = "images/tiny/" . $imagepath; //This is the new file you saving
              $file = "images/" . $imagepath; //This is the original file
 
              list($width, $height) = getimagesize($file) ; 
 
              $modwidth = 40; 
 
              $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) ; 
			  $sql = "UPDATE `users` SET image = '".$id.".".$file_ext."' WHERE ID=$id";
mysql_query($sql) or die(mysql_error());
			  
            echo "Large image: <img src='images/thumbs/".$imagepath."'><br>"; 
            echo "MINI: <img src='images/mini/".$imagepath."'>"; 
			echo "TINY: <img src='images/tiny/".$imagepath."'><br>";  
 
          }
        }
?>

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