function random_imglink(){
	
	var images=new Array();
	images[0]="images/masthead_1.gif";
	images[1]="images/masthead_2.gif";
	images[2]="images/masthead_3.gif";
	images[3]="images/masthead_4.gif";
	images[4]="images/masthead_5.gif";

    var ry=Math.floor(Math.random()*images.length);
  
   document.getElementById('masthead_main_img').src=images[ry];
}