Nasıl bir PHP Curl kullanarak başka bir web sitesine bir dosya yüklemek ve tepki sayfasını alır?

Web sitesi: http://www.postto.me

<form action="posttome.php" enctype="multipart/form-data" method="post">
<input type="hidden" value="2097152" name="MAX_FILE_SIZE">
<input type="file" size="30" class="input" name="img">
<input type="submit" class="input" value="Upload" name="upload">
</form>


<?php
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_HEADER, 0);
    curl_setopt($ch, CURLOPT_VERBOSE, 0);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/4.0 (compatible;)");
    curl_setopt($ch, CURLOPT_URL, "http://www.postto.me/upload.php");
    curl_setopt($ch, CURLOPT_POST, true);
    // same as <input type="file" name="file_box">
    $post = array(
        "img"=>$_FILES["img"]["tmp_name"],
    );
    curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
    $response = curl_exec($ch);
    echo $response;

echo $_FILES["img"]["tmp_name"];
}
?>

o [Nasıl] çalışmıyor?