var imagenumber = 4 ;
var randomnumber = Math.random() ;
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;
images = new Array
images[1] = "images/mastheadpic1.jpg"
images[2] = "images/mastheadpic2.jpg"
images[3] = "images/mastheadpic3.jpg"
images[4] = "images/mastheadpic4.jpg"
var image = images[rand1]