BUG: ngg_Thumbnail::show – wrong default parameter

function show($quality=100,$name = '') {
and also
ImageJpeg($this->newImage,'',$quality);

In both cases, instead of empty string (”), there should be null.

See here: http://www.php.net/manual/en/function.imagejpeg.php

To skip this argument in order to provide the quality parameter, use NULL.

http://wordpress.org/extend/plugins/nextgen-gallery/