php 判断图片文件的真实类型

/**
 *  * 检测文件的真实类型
 *   * @param  string $srcPath 文件路径
 *    * @return string $realType 文件真实类型
 *     */

$imgurl = 'http://pic.babytree.com/foto3/thumbs/2015/0506/51/8/357557aa334dd03923a408f_nb.jpg';

echo file_type_detect($imgurl);
function file_type_detect($srcPath){
    $types = array(
            => 'bmp',
            => 'gif',
            => 'mp3',
           => 'png',
          => 'jpg',
    );
    $curl_obj = new cURL(false);
    $binary = $curl_obj->get($srcPath);

    //$binary = file_get_contents($srcPath);
    $bytes = substr($binary, , );
    $head = @unpack('C2char', $bytes);
    $typeCode = intval($head['char1'].$head['char2']);
    $realType = isset($types[$typeCode]) ? $types[$typeCode] : $typeCode;
    return $realType;
}