Copyright of base assets

Copyright of base assets

I find the copyright information of the base assets somewhat incomplete.

Specifically, I would like to use student_c.png for my code entry. From the AUTHORS file I would guess that it is copyright by Jonathan Palecek. But it is very obviously based on male_walkcycle.png and male_pants.png by Stephen Challener, and hairmale.png by Manuel Riecke (re-dyeing probably done by Jonathan Palecek).

So how should I attribute that image?