The 2.0 fimware for the Cybook and Opus have new thumbnails for epub files.
They use the .thn extension and it is append after the .epub extension. This is
_6090.t2b thumbnails which use the book name without the extension
_6090.t2b appended to it. I have yet to start figuring out this new format
but at first glance it looks to be similar to the
What I have found is, if a
_6090.t2b file is present that will be used and the
.thn file will not be generated and the
_6090.t2b will be used as the
thumbnail. However, if both the
_6090.t2b and .thn are present then the .thn
will be used.