Book excerpt: "This project explores the role of photography in conceptual art practices during the 1960's and 1970's. Focusing each chapter on the work of a single, canonical figure -- Mel Bochner, Bruce Nauman, Douglas Huebler and John Baldessari -- Diack argues that these artists expanded the possibilities of the photograph as a "document of doubt," and played with the viewer's investment of truth and factuality in the medium"--