Most haunted house movies tend to falter in their conclusion when attempting to coalesce the supernatural goings on with a logical explanation. The Legend of Hell House is not an exception to that rule. However, up until that point, it's an effective thriller that exceptionally utilizes atmosphere and features quality work from it's four primary actors whose characters see their more sinister and sexual tendencies manifested by the provokings of the Belasco Mansion spirits.
Adapted from author/screenwriter Richard Matheson's (the I Am Legend novel, several notable Twilight Zone episodes, Duel) novel "Hell House", director John Hough and cinematographer Alan Hume create tension by peculiar framing--the four characters are often placed expressively or unnaturally within the same frame so that you can clearly see them all; and items and/or people are often situated right in front of the frame--as well as lighting that emphasizes fog and heavy color filtering, and an editing style that often cuts away from a scene a beat too early to an establishing shot that informs us the exact date and time of the following scene.
As mentioned earlier, there are only four significant characters in the entire film (and only about seven speaking roles in total), so it's kind of a shame that if given the right amount of attention, the viewer can gauge a major spoiler from FOX's DVD cover. And is the blue tint supposed to hide that particular character's identity or evoke the fog shrouded cinematography? Either way it fails.
I love (strike that, lurve) the above illustrated poster from the film's 1973 theatrical release that recalls a 1950's era EC comic cover but I do understand it may be too elusive or era specific to spark consumer interest. So instead, my recommendation is to go with the still below from early in the film when all four characters first enter the gates of Hell House. It not only displays the three main elements of the film: the house, the atmosphere and the characters, it also gives a sense of the unique compositions and style of the film. An added bonus, Edgar Wright paid homage to this specific shot in his faux Grindhouse trailer, Don't!