Result

jQuery

distance = 100;
sensitivity = 17;
var distHalf = distance / 2;

var parW = $('#par').width(),
    parH = $('#par').height();

$('.layer').each(function() {
    var layer = $(this);

    pixPos = distance * (layer.index() + 1);
    pixPosHalf = distHalf * (layer.index() + 1);

    layer.width('+=' + pixPos);
    layer.height('+=' + pixPos);
    layer.animate({left: '-' + pixPosHalf }, 0); 
    layer.animate({top: '-' + pixPosHalf}, 0); 
    
    wDiff1 = $('#par').width();
    hDiff1 = $('#par').height();
    wDiff2 = layer.width();
    hDiff2 = layer.height();

    var wDiff = ((wDiff2 / wDiff1) - 1).toFixed(2);
    var hDiff = ((hDiff2 / hDiff1) - 1).toFixed(2);

    $('#par').mousemove(function(mousEv) {
        parOffset = $(this).offset();
        mouseX = (mousEv.pageX - parOffset.left);
        mouseY = (mousEv.pageY - parOffset.top);
    });

    var parWhalf = parW / 2,
        parHhalf = parH / 2;
    var mouseX = parWhalf,
        mouseY = parHhalf;
    var posX = parWhalf,
        posY = parHhalf;

    setInterval(function() {
        posX += (mouseX - posX) / sensitivity;
        posY += (mouseY - posY) / sensitivity;
        layer.css({
            left: '-' + Math.round(posX * wDiff) + 'px',
            top: '-' + Math.round(posY * hDiff) + 'px'
        });
    }, 30);

});

css

#par{
    position:relative;
    margin:150px auto;
    width:400px;
    height:200px;
     overflow: hidden;
}
.layer{
   position:absolute;
    width:400px;
    height:200px;
    z-index: -2;
    background:url(http://public-domain-photos.com/free-stock-photos-4-big/travel/los-angeles/los-angeles-skyline.jpg);
}
.layer:hover{width:800px;height:400px;}
.layer p{position:relative;}

html

<div id="par">       
    <div class="layer l1">     
        
    </div>                     
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</div>

via

div要素で作る簡単なパララックス効果の応用