var imagenumber = 4 ; 
var randomnumber = Math.random() ; 
var rand1 = Math.round( (imagenumber-1) * randomnumber) + 1 ; 
images = new Array 
images[1] = "img/logo_pat.jpg"
images[2] = "img/logo_blej.jpg"
images[3] = "img/logo_bmc.jpg"
images[4] = "img/logo_wp.jpg"
var myimage = images[rand1]
document.write('<img src="' + myimage + '">')