可捕获的致命错误：类mysqli的对象无法在[关闭]中转换为字符串

i have this error i'm working to insert image to db but i m getting this error my code here

$sql="INSERT INTO uygulama 
            (no,baslik,aciklama,resimler,
            tur,kategori,yapimci,boyut,
            indirmelinki,APK,tarih) 
        VALUES(NULL, ?, ?, ?, "'.$db.'", ?, ?, ?, ?, ?, ?, NOW())";
$stmt=$db->prepare($sql);  
if ($stmt === false) die ("sorgu hatası".$db->error);

$stmt->bind_param("sssssssss", 
                $_POST['baslik'], $_POST['aciklama'], $_POST['resimler'], 
                $_POST['tur'], $_POST['kategori'], $_POST['yapimci'], 
                $_POST['boyut'], $_POST['indirmelinki'], $_POST['APK']);

$stmt->execute();
if (!$stmt) {
   die('Kayıt eklenmedi');
} else{
    echo "Başarıyla Kaydedildi";
}

}

echo "</div>";


## Uzantı Kontrollerim
$uzanti=    array('image/jpeg','image/jpg','image/png','image/x-png','image/gif');
## Aynı Dizinde Bulunan Resimler Klasörüne Kaydet
$dizin=     "app_images";
if(in_array(strtolower($_FILES['resimler']['type']),$uzanti)){ 
    move_uploaded_file($_FILES['resimler']['tmp_name'],"./$dizin/{$_FILES['resimler']['name']}");
    ## Türkçe Karakter Hatası
    $db = $_FILES['resimler']['name'];    
}

        <tr>
            <td>Resimler:</td>
            <td>
                <form enctype="multipart/form-data" method="post" action="" >
                    <input type="file" name="resimler" multiple="multiple" value=""/>
                </form><br/>
                <div id="goster"></div>
            </td>
        </tr>';

Why are you stuffing you DB object into your query string?

$sql = " .... ?, "'.$db.'", ?,...";
                   ^^^^

next time, try to actually READ the error message, and go look at the line of code it indicates where the error occurs. PHP doesn't spit out errors because it's having a bad hair day. It spits out errors because YOU committed an error.