I will try to showcase the basic design process that lead to the Warg (heads) seen in the film. This is actually one of the first things i did at Weta Workshop with ZBrush so excuse my rough as models! Weta Digital did an incredible job bringing them (and everything else in the film) to life. Most of this stuff is pretty standard production art, there wasn't a ton of time in most cases to do sexy paintings/renderings....but that's how it goes a lot of the time.
There were some initial designs done by the fantastic Nick Keller for this version of the film, but Peter seemed to respond to one of the Warg designs from a Gus Hunter environment painting (crop of which can be seen in lower right corner). My job initially was just to bring this into 3D as that's what we thought he was after. As this design looked very much just like a wolf and less like the hyena looking creatures from 'Lord of the Rings' i created a few other options that bridged the gap from the more wolf looking direction to the hyena looking ones seen in the earlier films. (i will spare your eyes from some of the mankier ones i did!)
First design trying to match the illustration.........and yes, i was asked to draw the glowing eyes and lines coming out of its eyes.