setInterval function is the one that has to be used. Here is an example for the same without any fancy fading option. Simple Javascript that does an image change every 30 seconds. I have assumed that the images were kept in a separate images folder and hence _images/ is present at the beginning of every image. You can have your own path as required to be set.
CODE:
var im = document.getElementById("img");
var images = ["_images/image1.jpg","_images/image2.jpg","_images/image3.jpg"];
var index=0;
function changeImage()
{
im.setAttribute("src", images[index]);
index++;
if(index >= images.length)
{
index=0;
}
}
setInterval(changeImage, 30000);