怎么样限制上传图片的格式呢？

<code>if($_SERVER['REQUEST_METHOD']=='POST'){
  if(is_uploaded_file($_FILES['up']['tmp_name'])){
    $path='./upload/';
    is_dir($path) || mkdir($path,0777,true);
    $type=ltrim(strchr($_FILES['up']['type'],'/'),'/');
    $fileName = time().mt_rand(0, 9999).'.'.$type;
    $fullpath = $path . $fileName;
    move_uploaded_file($_FILES['up']['tmp_name'], $fullpath);
  }
}</code>

<code>if($_SERVER['REQUEST_METHOD']=='POST'){
  if(is_uploaded_file($_FILES['up']['tmp_name'])){
    $path='./upload/';
    is_dir($path) || mkdir($path,0777,true);
    $type=ltrim(strchr($_FILES['up']['type'],'/'),'/');
    $fileName = time().mt_rand(0, 9999).'.'.$type;
    $fullpath = $path . $fileName;
    move_uploaded_file($_FILES['up']['tmp_name'], $fullpath);
  }
}</code>

<code><?php

//可以上传的类型
$arr_file_type = ['image/gif'];
//如果上传的类型 不在配置的类型数组里面
if(!in_array($_FILES['fileName']['type'],$arr_file_type))
{
    $msg ='文件类型有误！';
    return false;
}

</code>