if a image file is streamed by php, php should set the Expire header;
if it's static image file and served by lsws, should have the expire header.
you can check litespeedtech.com 's image header in pagespeed, can see expire header is there.
Sorry I missed you. I'm not good at it but I'm learning fast I'm using wordpress and have configured a subdomain for the media. Now the images (which do not have expire headers) are being served from the subdomain, does that still count as streaming through php ?