Lots and lots of lots of Photoshop and Grut Brushes.
I've had a couple of notes, "I like it but it's just tracing" - Thank you for those who inquired but no, it's not and here's why.
Take production stills, cut them apart, reposition as needed, mix different photos, add bits where they're missing. Then outline the trace image you want to see. Then take that outline and rework it with your own line work, adding removing, building a new world from the old, then add grey scale to build the tones you're looking for. When that's done, start painting. Now this particular image as 4 other cousins that never will see the light of day, nor if you placed it against the original production image would you see the same lines or even shapes, a lot has been added to go from 'tracing' to illustration.
For real world examples I would strongly suggest checking the work of The one and only Drew Struzan. You know him even if you don't.
[ www.google.com/search?q=drew+s… ]
This is the exact same technique he uses. Only he's a zen master and I'm grasshopper.
For what it's worth.