var imagenumber = 4 ;
 var randomnumber = Math.random() ;
 var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ;
 images = new Array
 images[1] = "http://www.sha-web.org/images/home1.jpg"
 images[2] = "http://www.sha-web.org/images/home2.jpg" 
 images[3] = "http://www.sha-web.org/images/home3.jpg" 
 images[4] = "http://www.sha-web.org/images/home4.jpg" 
 var image = images[rand1]