Serving direct static image vs via php

[etrader]

Serving static files is the native behavior of nginx, and when we use
gateway for scripting, it needs more works by nginx. Thus, loading a php
file should take more time than loading an image file.

I compare the speed of loading an image file with serving via php by

$image=imagecreatefromjpeg($imagepath);
header('Content-Type: image/jpeg');
imagejpeg($image);

Surprisingly (at least to me), the speed of loading the image via php
was 50 - 70% faster than loading the original image file directly. What
is the reason for this peculiar behavior?

I tested with Pingdom. The difference was in Receive step, which is
associated with downloading the data.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,224228,224228#msg-224228