var myPix = new Array ("images/banners/1.jpg","images/banners/2.jpg","images/banners/3.jpg","images/banners/4.jpg","images/banners/5.jpg","images/banners/6.jpg","images/banners/7.jpg","images/banners/8.jpg","images/banners/9.jpg","images/banners/10.jpg","images/banners/11.jpg","images/banners/12.jpg","images/banners/13.jpg")   
        
function choosePic(){
  if (document.images){
    randomNum=
    Math.floor((Math.random()*13))%13
    document.myPicture.src=myPix[randomNum]
  }
}