How to make a sliding thingamajig between photos?
<p>See the effect in the photos in the article here:</p>

<p><a href="http://www.popsci.com/science/article/2012-11/and-after-images-show-hurricane-sandys-devastation" rel="nofollow">http://www.popsci.com/science/article/2012-11/and-after-images-show-hurricane-sandys-devastation</a></p>

<p>Does anyone have any idea how that's done? I suppose I could make two frames with adjustable width within a fixed frame, but what about the handle? And the way the frame line and handle brighten and enlarge when you mouse over? Hover event, to be sure, but what kind of hover event?</p>
