Jennings' photography went from personal to practical to professional. Because of his photographic bent, the Pennsylvania Railroad began using his skills to survey construction sites and to track construction progress. This became common practice, and Jennings called it "Progressive Photography." He also mastered the art of photographing ships setting out for pleasure cruises, and his talent enticed cruise lines to hire him to take professional photographs to be used for marketing purposes. His reputation in commercial photography earned him an invitation to take commercial photos aboard the Titanic, but prior commitments prevented him from accepting this offer. While doing work aboard the "Empress of Ireland" cruiseliner, Jennings learned of the sinking of the Titanic, having narrowly escaped the ill-fated voyage. Though his name surfaces on its passenger list, he never set foot on the decks of the White Star Line's "unsinkable" ship.