Why am I getting [BLOB - 0] when I insert an image into a database using prepared statements?

Question

Hi all,

This one's been puzzling me for a bit; hope folks can offer some suggestions!

I'm uploading some video details and a thumbnail image to a database using prepared statements. When I do the upload, everything appears to work perfectly -- no SQLi errors or anything -- yet, when I look at the database, I notice that my image_contents field (which is a BLOB) reads [BLOB - 0], which suggests that it's empty.

On a hunch, I print_r'd both the $_POST and $_FILES arrays, as well as file_get_contents($_FILES['thumbnail_file']['tmp_name']). All fields are filled properly, and the file_get_contents() returns crazy-looking characters, which I assume means that it works as well. So, I'm a bit stumped. Here's the code I'm using:

    function add_new_video() {
    $image = $_FILES['thumbnail_file']['tmp_name']; // pass this file name to getimagesize() to determine the mime-type
    $size_array = getimagesize($image);
    $thumbnail_mimetype = $size_array['mime'];
    $thumbnail_contents = file_get_contents($image);
    $thumbnail_filesize = $size_array[3];
    $thumbnail_filename = $_FILES['thumbnail_file']['name'];

 $title = $_POST['title'];
 $summary = $_POST['summary'];
        // Checkbox...   
        if(!empty($_POST['demo_reel'])) {
  $demo_reel = $_POST['demo_reel'];
 }
 else {
  $demo_reel = 0;
 }

 $query = "INSERT INTO videos (title, summary, thumbnail_filename, thumbnail_filesize, thumbnail_mimetype, thumbnail_contents, demo_reel) VALUES(?, ?, ?, ?, ?, ?, ?)";
 if($stmt = $this->conn->prepare($query)) {
  $stmt->bind_param('sssssbi', $title, $summary, $thumbnail_filename, $thumbnail_filesize, $thumbnail_mimetype, $thumbnail_contents, $demo_reel);
  $stmt->execute();
  if($stmt->affected_rows == 1) {
   return true;
  }
  else {
   return false;
  }
 }
}

Thanks for reading, and any advice is greatly appreciated!