Caching images in browser with URL parameters and XSendFile

Try to use this kind of header (PHP code) with for example header('Cache-Control: must-revalidate'); for download a private files

$mime_types = array(        'pdf' => 'application/pdf',        'txt' => 'text/plain',        'html' => 'text/html',        'exe' => 'application/octet-stream',        'zip' => 'application/zip',        'doc' => 'application/msword',        'xls' => 'application/vnd.ms-excel',        'ppt' => 'application/vnd.ms-powerpoint',        'gif' => 'image/gif',        'png' => 'image/png',        'jpeg' => 'image/jpg',        'jpg' => 'image/jpg',        'php' => 'text/plain'        );if ($mimeType == '') {    $file_ext = strtolower(substr(strrchr($file_path.$file_name_gen, '.'), 1));    if(array_key_exists($file_ext, $mime_types)) $mime_type = $mime_types[$file_ext];    else $mime_type = 'application/force-download';    }ob_start();header('Content-Disposition: attachment; filename="' . $file_name_gen . '"');header('Content-Type: '.$mime_type);header('Expires: 0');header('Cache-Control: must-revalidate');header('Pragma: public');header('Content-Length: ' . filesize($file_path.$file_name));ob_clean();flush();readfile($file_path.$file_name);

And use Cache control with a best option for your solution like

Cache-Control: max-age=<seconds>Cache-Control: max-stale[=<seconds>]Cache-Control: min-fresh=<seconds>Cache-Control: no-cache Cache-Control: no-storeCache-Control: no-transformCache-Control: only-if-cached

BTW. $file_name_gen is a genuine file name on the server and $file_name is a file name users see for more file privacy.

For the record, this is mostly due to the fact the default value of session.cache_limiter is nocache.

See http://php.net/manual/en/function.session-cache-limiter.php on how to set a different value that fits your needs.

How do you generate the images? Do you have a public local directory or it is loaded by a CDN (remotely)?

Maybe it can help: HOW TO CACHE IMAGES GENERATED BY PHP