var currentPhoto = 0;
if( imageArr.length >= 2 ) {
  var secondPhoto = 1;
  var preImgs = new Array();
  for(var i=0;i<imageArr.length;i++) {
    preImgs[i] = new Image();
    preImgs[i].src = '/cms/pic2/800x288/baner/' + imageArr[i];
  }
}
else var secondPhoto = 0;

function changePic() {
  var newPos = 0;
  if( currentPhoto < (imageArr.length - 1) ) newPos = currentPhoto + 1;
  $("#header").css("background-image","url('/cms/pic2/1024x288/baner/"+ imageArr[newPos] +"')");
  currentPhoto = newPos;
}

$(document).ready(function() {
  if(imageArr.length > 2)
    setInterval("changePic()",3000);
});