Not long after they got married in the early 1990s, Sharon Kelly-North and her new husband, David North, were invited to Sharon's grandmother's tidy brick home in Seattle. Mattie Lyle was almost in her 90s by then and — likely inspired by a photo slideshow the newlyweds had recently put together — she enlisted them to help her go through a hat box filled with old photographs of her own. After being a hobbyist photographer for most of her life, Mattie had stacks of old snapshots to sort through — black-and-white remnants of a life well-lived. Somewhere in the box, there was a photo...