I also did a web banner for the official facebook page. You can check it out at https://www.facebook.com/Homeguard2013?notif_t=fbpage_fan_invite. I recommend everyone does.
The idea behind this is that by making the brain into a puzzle its a direct reference as to people might not understand it and it takes a while to piece it together, similiar to in the film conversations are always held and bits pieced together to work out emotions etc.
By having a piece missing this symbolizes that perhaps its not complete – a metaphor for the friendships developed between McMurphy and his peers. As McMurphy is different from his peers yet can still associate himself with the group, the missing piece has been put onto the spine and if you were to insert it in the gap in the puzzle it would fit but be a different colour containing a different meaning – that of a free mind perhaps.
I felt the need for a slight background on the back cover and i think the metal fence wiring works really well not only as a reference point to the film but if you notice it not where its supposed to be and looks upside down- symbolizing schizophrenia and things are not always what they seem which plays an important part in the film.