not masking image links

Hiya,

I’ve just started using this plugin and noticed that it isn’t masking the image links in my posts (although it is masking the text links!). Is there some way to make it mask both text and image links?

Problem page: http://www.joyokanjikai.com/books-on-japanese/

Best,
Brin

http://wordpress.org/extend/plugins/wp-noexternallinks/