php通过获取头信息判断图片类型的方法

$filename = '617.gif' ; function pictype ( $file ) {    /*$png_header = "/x89/x50/x4e/x47/x0d/x0a/x1a/x0a";    $jpg_header = "/xff/xd8";*/   $header = file_get_contents ( $file , 0 , NULL , 0 , 5 );    //echo bin2hex($header);    if ( $header { 0 }. $header { 1 }== "/x89/x50" )    {      return 'png' ;    }    else if( $header { 0 }. $header { 1 } == "/xff/xd8" )    {      return 'jpeg' ;    }    else if( $header { 0 }. $header { 1 }. $header { 2 } == "/x47/x49/x46" )    {      if( $header { 4 } == "/x37" )        return 'gif87' ;      else if( $header { 4 } == "/x39" )        return 'gif89' ;    } } echo pictype ( $filename );