function randomNumber(limit){
  return Math.floor(Math.random()*limit);
}

randomImage(['../images/fotos/1.jpg','../images/fotos/2.jpg','../images/fotos/3.jpg','../images/fotos/4.jpg','../images/fotos/5.jpg','../images/fotos/6.jpg','../images/fotos/7.jpg','../images/fotos/8.jpg','../images/fotos/9.jpg']); 

function randomImage(imgArr)
{
  var imgSrc, imgW, imgH, r;
  r = randomNumber(imgArr.length);

  imgSrc = imgArr[r];
  imgW = 188;
  imgH = 412;

  document.write('<IMG SRC='+imgSrc+' WIDTH='+imgW+' HEIGHT='+imgH+'>');
//  alert(imgSrc);
}