var rotationSpeed = 7000;
var containerName = "billboard";
var selElement = "img";
var imgContainer;
var currentImage;
$(document).ready(function() {
    imgContainer = $("#" + containerName);
    var randomStart = imgContainer.find(selElement).length;
    while (randomStart == imgContainer.find(selElement).length) {
        randomStart = Math.round(Math.random() * imgContainer.find(selElement).length);
    }
    currentImage = $(imgContainer.find(selElement)[randomStart]);
    imgContainer.find(selElement).css({
        zIndex: 8,
        position: "absolute",
        display: "none"
    });
    currentImage.show();
    currentImage.css("zIndex", 10);
    if(imgContainer.find(selElement).length > 1)
        setTimeout(rotateImages, rotationSpeed);
}); 
function rotateImages() {
    var nextImg = currentImage.next();
    if (nextImg.length == 0) { nextImg = imgContainer.find(selElement+":first"); }
    currentImage.css("zIndex", 9);
    nextImg.css("zIndex", 10);
    nextImg.fadeIn(1500, function() {
        currentImage.css("zIndex", 8);
        currentImage.hide();
        currentImage = nextImg;
        setTimeout(rotateImages, rotationSpeed);
    });
}