function random_img(){
  var mg=new Array()
  //specify random images below. You can have as many as you wish
  mg[1]="images/img1.jpg";
  mg[2]="images/img2.jpg";
  mg[3]="images/img3.jpg";
  	
 var r=Math.floor(Math.random()*mg.length);

  if (r==0) r=1;
 document.write('<img src="'+mg[r]+'" border=0 alt="img"></a>');
}