// retrieve blob content from database
$sql = "SELECT * FROM TravelImage WHERE ImageID=:id";
$statement = $pdo->prepare($sql);
$statement->bindParam(':id', $_GET['id']);
$statement->execute();

$result = $statement->fetch(PDO::FETCH_ASSOC);
if ($result) {
   // Output the MIME header
   header("Content-type: image/jpeg");
   // Output the image
   echo ($result["ImageContent"]);
}