img_to_output_via_memory.php

<?php

$h = fopen('php://memory', 'ab+');

$gd = @imagecreate(110, 20);

if (false === $gd) {
    throw new \RuntimeException('GD image is invalid');
}

$background_color = imagecolorallocate($gd, 0, 0, 0);
$text_color = imagecolorallocate($gd, 233, 14, 91);
imagestring($gd, 1, 5, 5, 'A Simple Text String', $text_color);

imagepng($gd, $h);

rewind($h);

header('Content-Type: image/png');
$stdout = fopen('php://output', 'rb');

stream_copy_to_stream($h, $stdout);

fclose($stdout);
fclose($h);