PHP can't display blob image from mysql

Question

I am a newbie in PHP, here is my code to show blob image type from database to a page :

<?php
   require_once('db.php');
   $conn = connect_db();
   $sql = "SELECT * FROM product WHERE user_id = '$id_active'";
   $result = mysqli_query($conn, $sql);
   $row = mysqli_fetch_array($result);
   header("Content-type: " . $row["image_type"]);
   echo $row["photo_url"];
?>

and here is the content of the database :

But in the webpage, it shows nothing :

I want to ask if I make any mistake ? Thanks in advance