How do I clear the cache

Hi
I´m trying to load a picture on my website, but when I remake the picture the browser shows the old one. How do I solve this? I think the problem lies in the cache: how do I clear it?

<?php
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
?>

Check Example #2 at http://php.net/manual/en/function.header.php

tried that, but it didn´t work!!

Add a querystring on the end of the image path

<?php
$nocache = rand(0,1000);
?>
<img src="image.png?<?php echo $nocache; ?>" />

it´s no the best solution, but it works!! Thz!!