How do I get the base64 code?

[Kornelius]

I need to send the code (secret key) by email, but I don't want to save it to disk.
Please add this instruction to the library description.

<img src="data:image/png;base64, <?=QRcode::png('This QR code :)')?>"  />

 or

<?php
ob_start();
QRcode::png('This QR code :)');
$imageData = ob_get_clean();
?>
<img src="data:image/png;base64, <?=$imageData?>"  />

The error says that the HEADER is already defined.