PHP+jQuery+Ajax实现多图片上传效果

<form id="imageform" method="post" enctype="multipart/form-data" action="upload.php">
    <div id="up_status" style="display:none"><img src="loader.gif" alt="uploading"/></div>
    <div id="up_btn" class="btn">
        <span>添加图片</span>
        <input id="photoimg" type="file" name="photoimg">
    </div>
</form>
<p>最大100KB，支持jpg，gif，png格式。</p>
<div id="preview"></div>

<script type="text/javascript" src="jquery.min.js"></script>
<script type="text/javascript" src="jquery.wallform.js"></script>

$(function(){
    $('#photoimg').die('click').live('change', function(){
        var status = $("#up_status");
        var btn = $("#up_btn");
        $("#imageform").ajaxForm({
            target: '#preview', 
            beforeSubmit:function(){
                status.show();
                btn.hide();
            }, 
            suess:function(){
                status.hide();
                btn.show();
            }, 
            error:function(){
                status.hide();
                btn.show();
        } }).submit();
    });
});

$path = "uploads/";
$extArr = array("jpg", "png", "gif");
if(isset($_POST) and $_SERVER['REQUEST_METHOD'] == "POST"){
    $name = $_FILES['photoimg']['name'];
    $size = $_FILES['photoimg']['size'];
    if(empty($name)){
        echo '请选择要上传的图片';
        exit;
    }
    $ext = extend($name);
    if(!in_array($ext,$extArr)){
        echo '图片格式错误！';
        exit;
    }
    if($size>(1001024)){
        echo '图片大小不能超过100KB';
        exit;
    }
    $image_name = time().rand(100,999).".".$ext;
    $tmp = $_FILES['photoimg']['tmp_name'];
    if(move_uploaded_file($tmp, $path.$image_name)){
        echo '<img src="'.$path.$image_name.'"  class="preview">';
    }else{
        echo '上传出错了！';
    }
    exit;
}
//获取文件类型后缀
function extend($file_name){
    $extend = pathinfo($file_name);
    $extend = strtolower($extend["extension"]);
    return $extend;
}