iPad和iPhone上不显示正文背景图像

我创建了一个在台式机上运行良好的网站，但在iPhone和iPad上没有显示背景图像。

我已经尝试删除选择图像的php脚本并重新编写代码以使用javascript设置背景，在这种情况下背景显示正确。

这是选择图像的php代码:

<?php
//if  doesn't exist, open the session
if(!isset($_SESSION))
{
    session_start();
}
//set coockie
setcookie("allweb","connected", time()+3600);
//if doesn' exist yet, I create a new array
if(!isset($_SESSION['arrayImage'])){
    $arrayImage = array(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15);
}else{// else I get from sessiom
    $arrayImage = $_SESSION['arrayImage'];  
}
//if already exist variable $picture, increment it
if(isset($_SESSION['picture']) && isset($arrayImage)){
    $picture=$_SESSION['picture'];
    $picture = $picture + 1;
    $_SESSION['picture'] = $picture;//save picture
}else{// else I create it
    $picture = 1;
    $_SESSION['picture'] = $picture;// save it
    shuffle($arrayImage);// I shuffle the array
    $_SESSION['arrayImage'] = $arrayImage;//save array to the session
}
?>

<style type="text/css">
<?php 
if($picture < 15){//if I'm not out fo bound I continue
    echo 'body {background-image:url("images/bg'.$arrayImage[$picture].'hq.jpg");}';
}
else{// else I set picture to default value and restar the loop.
    $picture = 0;
    $_SESSION['picture'] = $picture;// save it
    echo 'body {background-image:url("images/bg'.$arrayImage[$picture].'hq.jpg");}';
}       
?>      
</style>

问题是图像没有立即显示，但我必须缩放页面，然后它们出现。