Check the manual that corresponds to your MySQL server version?

Ваш вариант не работает. Fatal error: Uncaught mysqli_sql_exception: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ', '????\0JFIF\0\0`\0`\0\0??\0C\0 ' at line 2.

$query = "INSERT INTO newUser (FIO, Company, phone, email, birthday, photo)
VALUES('$fullname', '$company', '$phone', '$email', $birthday, '$photo')";

Check the manual that corresponds to your MySQL server version?

Дата задана как дата, поэтому на строковое значение ругается.