(function() {
    function load() {
        if (this.naturalWidth > this.clientWidth || this.naturalHeight > this.clientHeight) {

            this.style.cursor = "pointer";
            this.onclick = function() {

                var overlay = document.createElement("div");
                overlay.id = "overlay";
                overlay.onclick = function() {
                    document.body.removeChild(this);
                };

                var img = document.createElement("img");
                img.src = this.src;
                img.onload = function() {
                    img.style.marginLeft = -img.clientWidth / 2 + "px";
                    img.style.marginTop = -img.clientHeight / 2 + "px";
                    close.style.marginTop = -img.clientHeight / 2 - close.offsetHeight / 2 + "px";
                };

                var inner = document.createElement("div");
                inner.appendChild(img);
                overlay.appendChild(inner);

                var close = document.createElement("span");
                close.innerHTML = "close";
                inner.appendChild(close);

                document.body.appendChild(overlay);
            }
        }
    }
    var i, imgs = document.getElementsByTagName("img");

    for (i = 0; i < imgs.length; i++) {
        if (!imgs[i].naturalWidth) {
            imgs[i].onload = load;
        } else {
            load.call(imgs[i]);
        }
    }
}());