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;
    }
}