The CGI used for Paul Walker's unfinished scenes in Furious 7 is reportedly done so well you can't even tell which scenes were filmed before and after his death. Universal has declined to reveal how exactly this was done, but THR is reporting Peter Jackson's Weta Digital was given the "sensitive and arduous" task.
The Mill, a visual effects studio headquartered in London, previously used 2D compositing when actors passed away in Gladiator and The Sopranos. Now technology is capable of creating actors entirely from 3D deposits. The studio recently made a computer-generated Bruce Lee for a 90-second Johnny Walker ad in China.
"We created his entire face in CG and hand-animated that, using shots of the actor for reference," CEO Robin Shenfield told THR. "The eyes require a lot of work. Keeping motion continuous in the musculature and the eyes is the key to making it look real."
It's also possible that Furious 7 took 3D scans of Walker when the film first began. This was done on Captain America: The Winter Soldier so CG doubles can be used for stunt scenes. Scans have also been made purely for archival purposes, which could allow for Hollywood to pull a Tupac and bring back an actor years after their death.