1. Use JS to define an array of images that you want to display randomly

ar imgArr=["//www.jb51.net/logo_cn.png",
"//www.jb51.net/baidu_sylogo1.gif",
"//www.jb51.net/news/uploadImg/20120111/20120111081906_79.jpg",
 "//www.jb51.net/news/uploadImg/20120111/20120111081906_76.jpg"];

Please replace the above picture with your own.

2. Generate a random number with JS, starting from 0 and ending at imgarr.leng-1

var index =parseInt(Math.random()*(imgArr.length-1));

So we get the current randomly generated image

var currentImage=imgArr[index];

3. Since a background picture is generated randomly, use JS to take this picture as the background picture.

document.getElementById("BackgroundArea").style.backgroundImage="url("+currentImage+")";

Since this is a demo, I’ve defined a div on the page with an id of BackgroundArea and a random background for that div.

<div id="BackgroundArea">
</div>