how to cache image generated by php

Question

i made a file to print out the image file with W and H i define by get method

but my problem is to cache this pictures

i add this headers to the file

@header("Cache-Control: private, max-age=10800, pre-check=10800");
@header("Pragma: private");
@header("Expires: " . date(DATE_RFC822,filemtime($full_path)));

if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])
       &&
  (strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == filemtime($full_path))) {
  // send the last mod time of the file back
  header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($full_path)).' GMT',true, 304);
  exit;
}else
{
     @header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime($full_path)) . ' GMT');
     @header('Content-Type: image/jpeg');
     @imagejpeg($image);
}

but my problem is some pictures are cached ok , but others are not , and sometime pictures inside album not appear until if i disable the cache header

is my headers are correct ? , and about the cache do i have to use - or + to set the time cache how its work ?

Answer 1

because they use Htaccess with mod_expires?

Example #1:

# enable expirations
ExpiresActive On
# expire GIF images after a month in the client's cache
ExpiresByType image/gif A2592000
# HTML documents are good for a week from the
# time they were changed
ExpiresByType text/html M604800

Read This Documentation

Example #2:

ExpiresActive On
ExpiresDefault A0
ExpiresByType image/gif A2592000
ExpiresByType image/png A2592000
ExpiresByType image/jpg A2592000
ExpiresByType image/jpeg A2592000