Tambahkan :

 <?php echo filemtime(‘nama_image’) ?>

Contoh Penggunaan :

<img alt=”Line chart” src=”generated/demo1.png?<?php echo filemtime(‘generated/demo1.png’) ?>” style=”border: 1px solid gray;”>

 

Sumber : http://bytes.com/topic/php/answers/8358-how-force-browser-reload-image-server