Easy parallax with a few lines of JavaScript.

parallax.js

// Initialize Parallax
var parallax_el = document.querySelectorAll('[data-parallax]');
var speed = 0.25;

function updateElementPosition() {
    [].slice.call(parallax_el).forEach(function(el,i) {
        var speed = el.dataset.parallax || 0.25;
        var offset = (-(window.pageYOffset - el.offsetTop) * speed);
        el.style.transform = 'translate3d(0, ' + offset + 'px, 0)';
        el.style.OTransform = 'translate3d(0, ' + offset + 'px, 0)';
        el.style.msTransform = 'translate3d(0, ' + offset + 'px, 0)';
        el.style.MozTransform = 'translate3d(0, ' + offset + 'px, 0)';
        el.style.WebkitTransform = 'translate3d(0, ' + offset + 'px, 0)';
    });
}

if(window.innerWidth > 1024) {
    updateElementPosition();
    window.onscroll = function() {
        updateElementPosition();
    }
}

// Doesn't quite work...
// $.fn.parallax = function(strength) {
//     var scroll_top = $(window).scrollTop();
//     var move_value = Math.round(scroll_top * strength);
//     this.css('background-position', 'center -'+ move_value +'px');
// };