hnl.isVisible.js - jquery extension to check if an element is visible in the browser's viewport, demo: http://jsfiddle.net/49oownx6/111/

hnl.isVisible.js

$.fn.isVisible = function() {
    // Am I visible?
    // Height and Width are not explicitly necessary in visibility detection, the bottom, right, top and left are the
    // essential checks. If an image is 0x0, it is technically not visible, so it should not be marked as such.
    // That is why either width or height have to be > 0.
    var rect = this[0].getBoundingClientRect();
    return (
        (rect.height > 0 || rect.width > 0) &&
        rect.bottom > 0 &&
        rect.right > 0 &&
        rect.top < (window.innerHeight || document.documentElement.clientHeight) &&
        rect.left < (window.innerWidth || document.documentElement.clientWidth)
    );
};