The actor's character apparently died in the last season of the show, leading to a massive fan backlash, and theories/options for ways he could still return. While the show's producers have emphatically said, "Jon Snow is dead," Harington has been hinting that he might show up one way or another. In an interview with a Belgian Magazine, Humo, he said that "Game of Thrones will remain a part of my life for awhile."
The images seem to show Snow out of his Night's Watch blacks, however, and back in Stark leathers - could it be that this is just a scene from the past? That would let him return to the show and still be dead, after all.
So he's dead, but is he dead? Check out the set pictures at the link above yourself and start trying to figure out how Jon Snow could return.