Get an image from url in front end submission form

I am building a user generated content sharing theme
so how can i allow visitors to upload an image from a url
i mean to say that they enter the url and the image gets automatically attached

this is the code i am currently using for

<?php
/*
Template Name: Submit Content Template
*/

// if you are not using this in a child of Twenty Eleven, you need to replicate the   html structure of your own theme.

get_header(); ?>
<div id="primary">
        <div id="content" role="main">
<?php 
if(isset($_POST['new_post']) == '1') {
$post_title = $_POST['post_title'];
$post_category = 'todays_post';
$post_content = $_POST['post_content'];
$tags = $_POST['post_tags'];

$new_post = array(
  'ID' => '',
  'post_author' => $user->ID, 
  'post_category' => array($post_category),
  'post_content' => $post_content,
  'tags_input'    =>  array($tags),
  'post_title' => $post_title,
  'post_category' =>   array($_POST['cat']),  //
  'post_status' => '',
  'post_type' => 'post',
   'winerating' => $winerating
);


 $post_id = wp_insert_post($new_post);

    if (!function_exists('wp_generate_attachment_metadata')){
        require_once(ABSPATH . "wp-admin" . '/includes/image.php');
        require_once(ABSPATH . "wp-admin" . '/includes/file.php');
        require_once(ABSPATH . "wp-admin" . '/includes/media.php');
    }
     if ($_FILES) {
        foreach ($_FILES as $file => $array) {
            if ($_FILES[$file]['error'] !== UPLOAD_ERR_OK) {
                return "upload error : " . $_FILES[$file]['error'];
            }
            $attach_id = media_handle_upload( $file, $post_id );
        }   
    }
if ($attach_id > 0){
$post = get_post($post_id,'ARRAY_A');
$image = wp_get_attachment_image_src( $attach_id, 'large' );
$image_tag = '<p><a href="'.$image[0].'" rel="lightbox"  title="<?php the_title();?>" >   
<img src="'.$image[0].'" width="'.$image[1].'" height="'.$image[2].'" /></a></p>';

//add image under the content
$post['post_content'] = $image_tag . $post['post_content'];

//add image above the content
//$post['post_content'] = $post['post_content'] . $image_tag;

$post_id =  wp_update_post( $post );

}

// Update Custom Meta

// This will redirect you to the newly created post
$post = get_post($post_id);
wp_redirect( get_permalink($post_id));
exit();
}      
?>

UPDATE #1

 <?php
 /*
 Template Name: Submit Content Template
 */

  // if you are not using this in a child of Twenty Eleven, you need to replicate the          html structure of your own theme.

get_header(); ?>
<div id="primary">
        <div id="content" role="main">
<?php 


 if(isset($_POST['new_post']) == '1') {
 $post_title = $_POST['post_title'];
 $post_category = 'todays_post';
  $post_content = $_POST['post_content'];
 $tags = $_POST['post_tags'];
  $winerating = $_POST['winerating'];


   $new_post = array(
  'ID' => '',
  'post_author' => $user->ID, 
  'post_category' => array($post_category),
  'post_content' => $post_content,
  'tags_input'    =>  array($tags),
  'post_title' => $post_title,
  'post_category' =>   array($_POST['cat']),  //
  'post_status' => 'publish',
  'post_type' => 'post',
   'winerating' => $winerating
);


   $post_id = wp_insert_post($new_post);

 // Only for outside WP Theme; if you have this in a file you will need to load "wp- load.php" to get access to WP functions.  If you post to "self" with this code then WordPress is by default loaded
 require $_SERVER['DOCUMENT_ROOT'] . "/wp-load.php";
  // require two files that are included in the wp-admin but not on the front end.   These give you access to some special functions below.
 require $_SERVER['DOCUMENT_ROOT'] . "/wp-admin/includes/file.php";
 require $_SERVER['DOCUMENT_ROOT'] . "/wp-admin/includes/image.php";

 // required for wp_handle_upload() to upload the file
 $upload_overrides = array( 'test_form' => FALSE );

 global $current_user;
 get_currentuserinfo();
 $logged_in_user = $current_user->ID;

 // count how many files were uploaded
 $count_files = count( $_FILES['files'] );

 // load up a variable with the upload direcotry
 $uploads = wp_upload_dir();

 // foreach file uploaded do the upload
 foreach ( range( 0, $count_files ) as $i ) {

     // create an array of the $_FILES for each file
     $file_array = array(
        'name'     => $_FILES['files']['name'][$i],
        'type'     => $_FILES['files']['type'][$i],
        'tmp_name' => $_FILES['files']['tmp_name'][$i],
        'error'    => $_FILES['files']['error'][$i],
        'size'     => $_FILES['files']['size'][$i],
    );

    // check to see if the file name is not empty
    if ( !empty( $file_array['name'] ) ) {

        // upload the file to the server
        $uploaded_file = wp_handle_upload( $file_array, $upload_overrides );

        // checks the file type and stores in in a variable
        $wp_filetype = wp_check_filetype( basename( $uploaded_file['file'] ), null );   

        // set up the array of arguments for "wp_insert_post();"
        $attachment = array(
            'post_mime_type' => $wp_filetype['type'],
            'post_title'     => preg_replace('/.[^.]+$/', '', basename(        $uploaded_file['file'] ) ),
            'post_content'   => '',
            'post_author'    => $logged_in_user, // or use a static ID
            'post_status'    => 'publish',
            'post_type'      => 'attachment',
            'post_parent'    => $_POST['post_id'],
            'guid'           => $uploads['baseurl'] . '/' . $file_array['name']
        );

        // insert the attachment post type and get the ID
        $attachment_id = wp_insert_post( $attachment );

        // generate the attachment metadata
        $attach_data = wp_generate_attachment_metadata( $attachment_id,  $uploaded_file['file'] );

        // update the attachment metadata
        wp_update_attachment_metadata( $attachment_id, $attach_data );

                // this is optional and only if you want to.  it is here for  reference only.
                // you could set up a separate form to give a specific user the ability to change the post thumbnail
                // set_post_thumbnail( $_POST['post_id', $attachment_id );
     }
 }

   $post_id =  wp_update_post( $post );

// Update Custom Meta


// This will redirect you to the newly created post
$post = get_post($post_id);
wp_redirect( get_permalink($post_id));
exit();

}      
?>
<html>
<head>
<title>Add Your Funny Pics</title>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js"></script>
<script>
   var blank="http://upload.wikimedia.org/wikipedia/commons/c/c0/Blank.gif";
   function readURL(input) {
    if (input.files && input.files[0]) {
      var reader = new FileReader();

      reader.onload = function (e) {
          $('#img_prev')
         .attr('src', e.target.result)
          .height(100);
     };

     reader.readAsDataURL(input.files[0]);
   }
  else {
   var img = input.value;
     $('#img_prev').attr('src',img).height(200);
   }
  $("#x").show().css("margin-right","10px");
   }
 $(document).ready(function() {
  $("#x").click(function() {
  $("#img_prev").attr("src",blank);
  $("#x").hide();  
  });
  });
  </script>
<!--[if IE]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->
<style>
article, aside, figure, footer, header, hgroup,
menu, nav, section { display: block; }
#x { display:none; position:relative; z-index:200; float:right}
 #previewPane { display: inline-block; }
</style>

<meta charset=utf-8 />

<!--[if IE]>
<script src="http://html5shiv.googlecode.com/svn/trunk/html5.js"></script>
<![endif]-->

</head>
<body>

<form method="post" action="" enctype="multipart/form-data">

<p>
<span style="font-family:comic sans ms,cursive;"><span style="color: rgb(105, 105,    105);"><span style="font-size: 24px;"><strong>Add a Funny Pic</strong></span></span> </span></p><br />


<!----------<Upload Bar>----->

<span style="font-size:12px;">Pic File :- &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span>

<div style="position:relative;float:right;margin-top: -88px;"><span id="previewPane">
<img id="img_prev" src="#" alt="your image" />
<span id="x">[X]</span></div></div>

 <br />
        <fieldset>



<!----------</Upload Bar>----->


<br /> <br />
<!----------<Post Title>----->

<span style="font-size:12px;">Post Title :-&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span><input type="text" required="required" name="post_title" size="60" id="input-title" placeholder="Add A Title Here" class="rounded" />
<br>
<!----------</Post Title>----->
<br/>
<!--<post tags>-->

   <fieldset class="tags">

    <label for="post_tags">
<span style="font-size:12px;">Tags :- &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span></label>

       <input  type="text" class="rounded" placeholder="Add Some Tags To Get Higher Votes"value="" size="60" tabindex="35" name="post_tags" id="post_tags"  />

</fieldset>
<!--</post tags>-->
</br>
<!-- <post Category> -->

<fieldset class="category">

    <label for="cat">
<span style="font-size:12px;">Category&nbsp;&nbsp;&nbsp;&nbsp&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</span></h4></label><?php wp_dropdown_categories( 'tab_index=10&taxonomy=category&hide_empty=0' ); ?>


</fieldset>
<!-- </post Category> -->


<span style="font-size:12px;">Text Area</span></h4><br />
<textarea rows="5" name="post_content" cols="66" id="text-desc" ></textarea><br>
<input type="hidden" name="new_post" value="1" /> <br>
<div style="Float:right;"><input class="submitbutton" type="submit" name="submit" value="Add"  /><br><br></div>
</form>

  </body>
</div></div></div>
<!--// New Post Form -->
<?php get_footer(); ?>