Update: For clarification, there is also some concept art by the same artist for prior games including Halo 4.
While this should all be taken with a grain of salt, some of the concept art that was already used have been found by this particular artist. There are some intriguing stills that might further explain the story of Halo 5 as well as leak details of the locations of this games setting. The are was created by Nicolas Bouvier, lead concept artist for Halo 5.
Nicolas has also worked on games prior such as Halo 4 and RAGE as well as many different book covers.