The Collaborative International Dictionary of English v.0.48:

Photomechanical \Pho`to*me*chan"ic*al\, a.
   Pertaining to, or designating, any photographic process in
   which a printing surface is obtained without the intervention
   of hand engraving.
   [1913 Webster]

WordNet (r) 3.0 (2006):

photomechanical
    adj 1: of or relating to or involving various methods of using
           photography to make plates for printing