var imageArray = new Array();

 //You can replace these image file names with your own image names.
imageArray[0] = "image/jt8.png";
imageArray[1] = "image/pi.png";
imageArray[2] = "image/jt4.png";
imageArray[3] = "image/jt5.png";
imageArray[4] = "image/jt6.png";
imageArray[5] = "image/jt7.png";
imageArray[6] = "image/firefox.png";
imageArray[7] = "image/ulogo.jpg";

function ac_pic() {
var rand = Math.floor(Math.random()*6); //Generating a random number between 0 and 5 
var imgPath = "<img src='"+imageArray[rand]+"' alt=' ' border='0'/>";
document.getElementById("image").innerHTML = imgPath;
}

function all_pic() {
var rand = Math.floor(Math.random()*8); //Generating a random number between 0 and 7 
var imgPath = "<img src='"+imageArray[rand]+"' alt=' ' border='0'/>";
document.getElementById("image").innerHTML = imgPath;
}