php 判断上传类型 避免上传漏洞

function ($file_name,$pass_type=array('jpg','jpeg','gif','bmp','png')){
$yx_file = $pass_type;
$kzm = substr(strrchr($file_name,"."),1);
$is_img = in_array(strtolower($kzm),$yx_file);
if($is_img){
return true;
}else{
return false;
}
}