图片压缩的有关问题

$obj = new finfo(FILEINFO_MIME_TYPE);
$type = $obj->file($file);

switch($type){
    case 'image/gif': $img = imagecreatefromgif($file); break;
    case 'image/jpeg': $img = imagecreatefromjpeg($file); break;
    case 'image/png': $img = imagecreatefrompng($file); break;
    default: return false;
}