A dozen paintings hang from the white walls of a gallery at the Museum of Modern Art in Hayama, Kanagawa Prefecture. Mostly prewar works by artists involved in the Proletarian movement, who focused on depictions of factory and farm laborers, the paintings are like many others on display at the museum — except that alongside each is a small photograph showing the same works cracked, scratched and, in many cases, caked in dirt and paper pulp.