simple parallax effect

HTML

<div class="bg"></div>

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CSS

.bg {
  width: 100%;
  height: 200px;
  background: url('//placekitten.com/1000/300') no-repeat;
  border: 1px solid red;
}

JavaScript

$(window).scroll(function() {
    var scrolledY = -3 * $(window).scrollTop() / 2;
    $('.bg').css('background-position', 'left ' + (scrolledY) + 'px');
 });