Random image only to be applied once
<p>I want my website to show a random background image (which I've set up with javascript) but I don't want it to change again while the user is on the site.  At the moment it changes every time you click a link, but I'd rather it only change when you hit the Home button.</p>

<p>I think this other question is similar, but as I haven't used php much before, I was wondering if there was a javascript alternative? (or just something silly i missing here?)
<a href="http://stackoverflow.com/questions/14429795/choose-random-value-only-once">choose random value only once</a></p>

<p>Thanks</p>
