Thanks to our friends at QuarterQuell.org we have a peek at some of the concept art from Mockingjay Part 1. The concept artist works closely with the Production Designer (Phil Messina) and the Director (Francis Lawrence) to achieve the look of the film. Joanna Bush has done concept art for both The Hunger Games and Catching Fire (see it here). She was the one who actually created the concept for the painting of Rue that Peeta does on the training center floor in Catching Fire.
You can check out Joanna Bush's other work on her website here.