The Living exist in a world without a big picture, says Julie: "the big picture is gone and the people who drew it are all dead" (1.8.52). Now everyone is feeling lost. The Living need a big picture to guide them.
The Dead, on the other hand, totally have that covered. The Boneys are quite fond of pictures, because the he Dead have no memories, so they depend on photographs to remember. The thing with them is that they remember death. Death of the Living and death of the Dead. They keep stacks of photos of dead people and use them to manipulate the Dead. In a way, they're making a big picture out of smaller ones, by using them to give the Dead purpose and drive to keep on being Dead. In that sense, their big picture is their perspective, one in which death is inevitable. And if death is unavoidable, what's the point of life?
When the Living get back to really living, they have to counteract this. At the end of the novel, children tape up photos of life: "A girl climbing an apple tree. A kid spraying his brother with a hose. A woman playing a cello. A newborn deep in sleep" (3.1.38). Now, like the dead, they've got some perspective. They're creating a big picture of life.
Julie says, "You should always be taking pictures, if not with a camera then with your mind" (1.10.14), but Warm Bodies seems to be saying that we shouldn't keep pictures of death and destruction. Which raises a question: do we need to be selective about our memories in order to thrive?