Whoever the designer was, they were so enthralled by the concept that they didn't bother to see if anybody else "got it" without having it explained. The poster looks to me like Lord Dark Helmet with a black veil over his entire head, and then a small shot of Anakin peeking around him a la "where's waldo." The only thing really interesting to me is the giant scar on Anakin's eye. I haven't seen that in any of the footage so far.