While I can't say with complete certainly that the location of the above photos is 278 (there might be too many windows back there), there's no doubt about the photo below. Notice the wing extension, drain pipe, and arched window frames that can all be seen in photos I took of the back of the house in 2005. By the way, that's magic dealer Frank Ducrot, Frederick Eugene Powell, and the great coin magician T. Nelson Downs with our Harry.
While we're on the subject of backyards, check out the photos below, also from the NYPL Digital Gallery, of Houdini taking a dive into a swimming pool. While this is not 278, I can't help but wonder (hope) that these might be shots of Houdini at the Walker mansion in Laurel Canyon, California, which over the years has come to be known as the "Houdini Mansion".
While we know Houdini didn't own the Laurel Canyon house -- he and Bess rented a smaller house belonging to the estate across the street while he made movies in Hollywood -- he almost certainly spent time there, and his appearance in this pics looks to be correct for his movie star days. Also, the Walker mansion did have an outdoor swimming pool with white titles as we see in the pics (I have a shard of that tile), and the surrounding foliage looks very Laurel Canyon to me. It's a long shot, but it would be great to finally put Harry on that property, if even just for a quick swim.
NYPL Digital Gallery provides free and open access to over 700,000 images digitized from the The New York Public Library's vast collections, including illuminated manuscripts, historical maps, vintage posters, rare prints, photographs and more.