To celebrate the gallery's 20 years, Michael Hoppen unveils the treasures of his extraordinary private photography collection in the gallery's largest public exhibition to date. Presented over three floors, Finders Keepers brings to light 130 photographic gems, handpicked for their fascinating narrative, masterful technique and historical relevance, ranging from anonymous 19th century pictures to iconic post-war snapshots. Finders Keepers offers a unique journe…