missing CC-BY 3.0 licence

The “drawing” gallery/test uses toolbar icons under CC-BY 3.0 from:
http://www.fatcow.com/free-icons

However, CC-BY 3.0 states that the licence has to be included with copies of the work.

(Maybe some CC0-licenced icons can be found instead…)