Capturing PNG stream with PHP output buffer - php

Question

I am currently attempting to write a web service that generates a QR code for a given string. I am using PHP QR Code (http://phpqrcode.sourceforge.net/) to generate the QR code, like this:
QRcode::png('PHP QR Code :)');
Result: a PNG stream of the QR Code is displayed on the screen.
As this is a void function that outputs directly to the browser, this prevents me from properly returning the image.
I would like to capture the PNG stream with PHP's output buffer and have my web service return this captured image.
I have set up the following test code on a plain php page for testing purposes:
include('/vendor/phpqrcode/qrlib.php');
$scancode = "testcode";
ob_implicit_flush(false); //just in case
ob_start();
QRcode::png($scancode);
$output = ob_get_contents();
ob_end_clean();
echo "--" . $output . "--";
die();
However, when I run the code the buffer does not work as I had planned. No matter what I do, a broken image is always displayed as soon as I call the function. When I remove the output buffer code the QR code is rendered on the screen.
Why is some of my output not being captured?
Edit: related: phpqrcode library return image as a string

Answer 1

Remove header("content-type:image/png");
to get it worked with output buffering.
Later you can echo
header("content-type:image/png"); and your captured output to show the image