USA claim AQ have been using stenography since the 90s:

http://usatoday30.usatoday.com/tech/news/2001-02-05-binladen...

Commercial companies then built tools to identify most common steg, and AQ adapted by writing their own algorithms - which turned out to be not very good:

http://edition.cnn.com/2012/04/30/world/al-qaeda-documents-f...

It still breaks down, because you need to pre-share the arrangement of how you will exchange information that is hidden in images.