if ($_REQUEST['type']=='jpg') {
  header('Content-Type: image/jpeg');
} else if ($_REQUEST['type']=='png') {
  header('Content-Type: image/png');
}

HTTP/1.1 200 OK
Date: Mon, 27 Jun 2016 05:23:58 GMT
Server: Apache/2.2.31 (Amazon) DAV/2 PHP/5.3.29
X-Powered-By: PHP/5.3.29
Expires: Tue, 27 Jun 2017 05:23:58 GMT
Cache-Control: max-age=31536000
Last-Modified: Tue, 28 Apr 2015 21:30:32 GMT
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 1887
Connection: close
Content-Type: image/png

HTTP/1.1 200 OK
Date: Mon, 27 Jun 2016 05:23:18 GMT
Server: Apache/2.2.31 (Amazon) DAV/2 PHP/5.3.29
X-Powered-By: PHP/5.3.29
Expires: Tue, 27 Jun 2017 05:23:18 GMT
Cache-Control: max-age=31536000
Vary: Accept-Encoding
Content-Encoding: gzip
Content-Length: 15704
Connection: close
Content-Type: