var upperLimit = 99;
var imagePath = "http://www.bloggerindia.com/ad/";
var baseName = "";
var imageType = ".jpg";
var randomNum = Math.round(Math.random()*upperLimit);
var fileName = imagePath + baseName + randomNum + imageType;
//return fileName; 
document.write("<img src='"+fileName+"' width=40 height=40>");