scaladoc in Netbeans 6.9.1

Probably an easy question:
how can I skip image files whene generating the scaladoc (using the
context menu of the Netbeans plugin for scala) ...

otherwise I get a decoding error (error: IO error while decoding
/home/pezzatti/wsl/dev/fireindices/guiFireIndices/src/org/wsl/fireindices/gui/res/alpffirs.gif
with UTF-8) since the compiler want to build a scaladoc also for the
images ...

Thanks
Boris