How to get the browser to cache images, with PHP?

Question

I'm totally new to how to cache images.

I output all images in a gallery with PHP, and want the images already shown, to be cached by the browser, so the PHP script don't have to output the same image again. All I want is the images to show up faster.

When calling an image I do like this:

<img src="showImage.php?id=601"> 

and the showImage.php-file does:

$id = (int) $_GET['id']; $resultat = mysql_query("     SELECT filename, id     FROM Media      WHERE id = $id "); $data = mysql_fetch_assoc($resultat);  ...  //Only if the user are logged in if(isset($_SESSION['user'])){     header("Content-Type: image/jpeg");      //$data['filename'] can be = dsSGKLMsgKkD3325J.jpg     echo(file_get_contents("images/".$data['filename'].""));  } 

Answer 1

First of all, if you're using sessions, you must disable session_cache_limiter (by setting it to none or public). Headers it sends are pretty bad for caches.

session_cache_limiter('none'); 

Then send Cache-Control: max-age=number_of_seconds and optionally an equivalent Expires: header.

header('Cache-control: max-age='.(60*60*24*365)); header('Expires: '.gmdate(DATE_RFC1123,time()+60*60*24*365)); 

For the best cacheability, send Last-Modified header and reply with status 304 and empty body if the browser sends a matching If-Modified-Since header.

header('Last-Modified: '.gmdate(DATE_RFC1123,filemtime($path_to_image))); 

For brevity I'm cheating here a bit (the example doesn't verify the date), but it's valid as long as you don't mind browsers keeping the cached file forever:

if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) {    header('HTTP/1.1 304 Not Modified');    die(); }