By Keith F. Davis Foreword by Donald J. Hall Hallmark Cards/Harry N. Abrams, Inc., New York 608 pages; 499 b&w and color illustrations; $95Innovation/Imagination: Fifty Years of Polaroid PhotographyIntroductions by Barbara Hitchcock and Deborah Klochko Essay by Deborah Martin Kao Friends of Photography/Harry N. Abrams, Inc., New York 120 pages; 90 color photographs; $35In his thorough and lucid text of An American Century of Photography, Keith Davis reminds us that Americans made 17 billion...