 <p>One answer is to hackishly add some get query parameter like has been suggested.</p> <p>A better answer is to emit a couple of extra options in your HTTP header.</p> <pre><code>Pragma: no-cache Expires: Fri, 30 Oct 1998 14:19:41 GMT Cache-Control: no-cache, must-revalidate </code></pre> <p>By providing a date in the past, it won't be cached by the browser. <code>Cache-Control</code> was added in HTTP/1.1 and the must-revalidate tag indicates that proxies should never serve up an old image even under extenuating circumstances, and the <code>Pragma: no-cache</code> isn't really necessary for current modern browsers/caches but may help with some crufty broken old implementations.</p>