JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.9/themes/start/jquery-ui.css" type="text/css" media="all" />
<div id="#wrapper">
    <div id="x">
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
        <img src="http://www.barneyb.com/barneyblog/wp-content/themes/hybrid/library/images/pingback.png" />
    </div>
</div>

CSS

img{
    margin-bottom:5px;
    opacity:0.2;
}
#x{
    width:1000px;
    height:100px;
}
div{
    width:250px;
    height:120px;
    overflow-x:auto;  
}

JavaScript

var $div = $('div');
var divleft = $div.position().left;
$('div').scroll(function() {
    $('img').each(function() {
        img = $(this);
        imgleft = img.position().left;
        if (imgleft >= divleft && imgleft + img.width() <= divleft + $div.width()) {
            $(this).css({
                opacity: '1'
            })
            $(this).siblings('img').css({
                opacity: '0.2'
            });
            return false;
        }
    });
})