send imagick captcha to client with font cause apache "dead"

$image = new \Imagick();
$draw = new \ImagickDraw();

$fillColor = new \ImagickPixel('black');
$bgColor = new \ImagickPixel('gray');
$fontSize = 24;
$text = 'helloworld';
$text = substr($text, 0, rand(1, 10));
$font = '/home/koogua/font/yy.ttf';

$draw->setFont($font);
$draw->setFontSize($fontSize);
$draw->setFillColor($fillColor);
$draw->setStrokeAntialias(true);
$draw->setTextAntialias(true);
$draw->setgravity(\Imagick::GRAVITY_CENTER);
$draw->annotation(0, 0, $text);

$metrics = $image->queryFontMetrics($draw, $text);

$image->newImage($metrics['textWidth'] + 30, $metrics['textHeight'] + 10, $bgColor);
$image->setImageFormat('png');
$image->drawImage($draw);

$draw->destroy();

// $image->writeImage('test.png');

header('Content-Type: image/png');
echo $image->getImageBlob();
exit;

 // $this->response->setContentType( 'image/png');
 // $this->response->setContent($image->getImageBlob());
 // $this->response->send();

enviroment: phalcon

output with font : refresh the page 1- 5 times, capcha image is ok, after 5 times, apache "dead"

output without font : ok

save file : ok

enviroment: another php framework (rewrite is enabled)

output with font : ok

output without font : ok

save file: ok

enviroment: pure php

output with font : ok

output without font : ok

save file: ok

can someone test the above code ?

stackoverflow discussion link: https://stackoverflow.com/questions/32556611/output-captcha-image-with-font-cause-apache-dead