Simply Photoshop skills......the haze would be the easiest part. Layers of a gradient going from white at the bottom to transparent at the top, then different optimacey settings. Probably a bit more jigging around, same or different titan photoed in different stances layered on with the gradient layer in between each, giving the sense of more fade in the distance.
The rest is where the more artistic skills come in to play, and are probably painted on by a digital artist.