"1984" is about censorship, a totalitarian government, the idea fo being watched and the absurd nature of such a world. These were visualized in the form of thumbnail sketches.
More research showed that the first line of the novel, "It was a bright cold day in April and the clocks were striking thirteen" was the most famous line of the novel, and also the well-known for being the best opening line of any novel as it establishes the context of the book so well. This was developed into a book cover idea.