Koken calculates and returns a Content-Length header, regardless of the server is going to compress/chunk the response.

[koken] disable_Content-Length.diff

commit 74ae5fa6e841bbe1092cf6262fb6031b44fa9b4c
Author: Hereward Cooper <coops@fawk.eu>
Date:   Mon Jul 14 14:46:17 2014 -0700

    disabling content-length header

diff --git a/i.php b/i.php
index a6c704e..52446b2 100755
--- a/i.php
+++ b/i.php
@@ -416,7 +416,6 @@
 	}
 
 	header('Content-type: image/' . $ext);
-	header('Content-length: ' . filesize($file));
 	header('Cache-Control: public');
 	header('Expires: ' . gmdate('D, d M Y H:i:s', strtotime('+1 year')) . ' GMT');
 	header('Last-Modified: ' . gmdate('D, d M Y H:i:s', filemtime($file)) . ' GMT');
@@ -426,4 +425,4 @@
 		readfile($file);
 	} else {
 		die(file_get_contents($file));
-	}
\ No newline at end of file
+	}