Question

I have a script that is generating an image with PHP on a server, in the form of image.png. I’m then using this image in different places using <img src="http://domain.com/images/image.png" />.

The problem I’m running into is that even though the image is being regenerated every 30 minutes, it seems to be cached and won’t show the new values until I go to http://domain.com/images/image.png and then ctrl+shift+refresh.

Is there any way I can keep the image name the same, but make it always show the newest version of the image?

Answer 1

There are a few options, depending on your situation. If “images/image.png” is an actual file on the server and you are accessing it directly, then you have to change the cache settings on the folder or use .htaccess to inform a browser to resend it.

<FilesMatch "\.(ico¦pdf¦flv¦jpg¦jpeg¦png¦gif¦js¦css¦swf)$">
ExpiresDefault A604800
Header set cache-control: "no-cache, public, must-revalidate"
</FilesMatch> 

If you are using PHP to find the image and returning it, you can use PHP to send headers.

header("Expires: ".gmdate("D, d M Y H:i:s", time()+1800)." GMT");
header("Cache-Control: max-age=1800");

To do it perfectly with PHP, you can check if its actually modified

$last_modified_time = @filemtime($file);
header("Expires: ".gmdate("D, d M Y H:i:s", $last_modified_time+1800)." GMT"); 
//change with $last_modified_time instead of time().
//Else if you request it 29mins after it was first created, you still have to wait 30mins
//but the image is recreated after 1 min.

header("Cache-Control: max-age=1800");
header("Vary: Accept-Encoding");

// exit if not modified
if (array_key_exists('HTTP_IF_MODIFIED_SINCE', $_SERVER)) {
    if (@strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == $last_modified_time) { 
        header("HTTP/1.1 304 Not Modified"); 
        return;
    }
}