The (custom) smileys are located in /wp-includes/images/smilies/. I don’t think a wp-includes folder in the child themes’ folder adds an alternative smiley directory.
I made the changes according to this guide
http://www.mustbeweb.com/how-to-add-custom-emoticons-in-wordpress/
Maybe you can integrate the jpegoptim plugin as well? (I did not check it’s success rate compared to jpgtran )
Several guides said it is working .. Even if WordPress needs these images, it should be possible to modify it…
