var imagenumber = 6 ;
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;

images = new Array;
images[1] = "images/tiles01.jpg";
images[2] = "images/tiles02.jpg";
images[3] = "images/tiles03.jpg";
images[4] = "images/tiles04.jpg";
images[5] = "images/tiles05.jpg";
images[6] = "images/tiles06.jpg";

var image = images[rand1];