From Framestore press release:

Steven Spielberg’s War Horse opened on Christmas Day in the US, and on 13th January 2012 in the UK. Based on Michael Morpurgo’s 1982 novel, the film stars Jeremy Irvine, Emily Watson, Peter Mullan and David Thewlis. The screenplay is by Richard Curtis and Lee Hall, based on both the novel and Nick Stafford’s stage version. The cinematography is by Janusz Kamiński, and the film was produced by Spielberg and Kathleen Kennedy. Framestore is the film’s sole provider of digital visual effects, delivering just over 200 shots to the movie.

War Horse tells the story of Joey, a horse born in Devon shortly before the start of the First World War. Belonging to – and beloved by - a young man, Albert Narracott, Joey is sold to the cavalry and shipped to France at the outbreak of war. Joey serves in the British and German armies, which takes him on an extraordinary odyssey, serving on both sides before finding himself alone in No Man's Land. But Albert has not been able to forget Joey and, still not old enough to enlist in the British Army, he has embarked on his own dangerous mission to find the horse and bring him home to Devon.

Steven Spielberg decided to create his film after he and Kennedy had seen the enormously successful stage version of the book. But, where the theatrical telling involves the use of extraordinary horse puppets to bring the equine cast to life, Spielberg knew that a cinematic story would need to use a different language. For the big screen, Spielberg decided that only a ‘realistic’ approach would do – one in which as much of the action as possible was captured in camera, as it happened on location. He was aiming for a style such that the film might have been made half a century ago, in sympathy with its historical distance, so there is no modern ‘tricksiness’ on view. That said, he knew that the story would require a few feats that would be impossible to capture safely with a live animal, and for which only the very best digital equine doubling would suffice. Enter Framestore.

More than half of Framestore’s 200 or so shots involved clean-up or similar work – vapour-trail removal, telephone wire removal and the like. More elaborate labour and skills were required to remove riders from horses or augment a huge field of reeds in which British soldiers conceal themselves prior to an attack. Just as challenging was the harrowing sequence towards the end of the film in which Joey, struggling through the trenches, is finally brought down to the ground as he drags a mess of barbed wire and a broken gate behind him: the horse was real, but the wires could not be. Finally, for just a couple of shots, digital horses were going to be needed – ones good enough to trick the eye of Steven Spielberg…

Ben Morris, Framestore’s VFX Supervisor on the project, recalls, “Kathleen Kennedy (Spielberg’s long-time producer) and his Production Designer, Rick Carter, came to meet us. It went really well, I think, because they quickly recognized that we could deliver everything they needed, from the mundane, to state of the art CG animation. I should emphasise that the film Steven wanted to make had no place for self-conscious VFX shots – it was to be as real as possible, with any digital elements integrated invisibly in the service of that sensibility.”