if (strlen($row["isbn13"]) == 13) {
            $command .= "http://covers.openlibrary.org/b/isbn/" . $row["isbn13"] . "-L.jpg";
        } elseif (strlen($row["isbn10"]) == 10) {
            $command .= "http://covers.openlibrary.org/b/isbn/" . $row["isbn10"] . "-L.jpg";
        }
        exec($command);
        $command = "mv " . $row["book_id"] . ".jpg covers/" . $row["book_id"] . ".jpg";
        exec($command);
        $updateQuery = "UPDATE books SET has_cover=1 WHERE book_id='" . $row["book_id"] . "'";
        mysqli_query($connection, $updateQuery);
    }
    array_push($output["table_data"], $result);
}
if (empty($output["table_data"])) {
    // book not in urBooks database
    if ($usedISBN && checkOpenLibrary($bookISBN, $connection)) {
        $data = mysqli_query($connection, $queryString);
        $output["table_data"] = array();
        while ($row = mysqli_fetch_array($data)) {
            $result = array();
            $result["title"] = $row["title"];
            $result["isbn13"] = $row["isbn13"];
            $result["isbn10"] = $row["isbn10"];
            $result["book_id"] = $row["book_id"];
            $result["year"] = $row["year"];
            $result["author"] = $row["author"];
            $result["has_cover"] = $row["has_cover"];
            // Download cover .jpg from OpenLibrary
            if ($row["has_cover"] == null) {
                $command = "wget -O " . $row["book_id"] . ".jpg ";
                if (strlen($row["isbn13"]) == 13) {
         $command = "wget -O " . $row["book_id"] . ".jpg ";
         if (strlen($row["isbn13"]) == 13) {
             $command .= "http://covers.openlibrary.org/b/isbn/" . $row["isbn13"] . "-L.jpg";
         } elseif (strlen($row["isbn10"]) == 10) {
             $command .= "http://covers.openlibrary.org/b/isbn/" . $row["isbn10"] . "-L.jpg";
         }
         exec($command);
         $command = "mv " . $row["book_id"] . ".jpg covers/" . $row["book_id"] . ".jpg";
         exec($command);
         $queryString = "UPDATE books SET has_cover=1 WHERE book_id='" . $row["book_id"] . "'";
         mysqli_query($connection, $queryString);
     }
     array_push($output["table_data"], $result);
 }
 if (empty($output["table_data"])) {
     if ($usedISBN && checkOpenLibrary($scanned_isbn, $connection)) {
         $data = mysqli_query($connection, $queryString);
         $output["table_data"] = array();
         while ($row = mysqli_fetch_array($data)) {
             $result = array();
             $result["title"] = $row["title"];
             $result["isbn13"] = $row["isbn13"];
             $result["isbn10"] = $row["isbn10"];
             $result["book_id"] = $row["book_id"];
             $result["year"] = $row["year"];
             $result["author"] = $row["author"];
             $result["has_cover"] = $row["has_cover"];
             if ($row["has_cover"] == null) {
                 $command = "wget -O " . $row["book_id"] . ".jpg ";
                 if (strlen($row["isbn13"]) == 13) {
                     $command .= "http://covers.openlibrary.org/b/isbn/" . $row["isbn13"] . "-L.jpg";