The Collaborative International Dictionary of English v.0.48:

Photo \Pho"to\ (f[=o]"t[-o]), n.; pl. Photos (f[=o]"t[-o]z).
   A contraction of Photograph. [Colloq.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Photo- \Pho"to-\ (f[=o]"t[-o]-).
   A combining form from Gr. fw^s, fwto`s, light; as,
   photography, phototype, photometer.
   [1913 Webster]

WordNet (r) 3.0 (2006):

photo
    n 1: a representation of a person or scene in the form of a
         print or transparent slide; recorded by a camera on light-
         sensitive material [syn: photograph, photo, exposure,
         picture, pic]

Moby Thesaurus II by Grady Ward, 1.0:

44 Moby Thesaurus words for "photo":
   3-D, Telephoto, Wirephoto, aerial photograph,
   black-and-white photograph, candid photograph, cheesecake,
   chronophotograph, color photograph, color print, diapositive,
   heliochrome, heliograph, montage, mug, mug shot, panchromatic,
   photoactive, photobiography, photochronograph, photogenic,
   photograph, photographic, photomap, photomicrograph, photomontage,
   photomural, photosensitive, picture, pinup, portrait, shoot, shot,
   slide, snap, snapshot, still, still photograph, telephoto,
   telephotograph, telephotographic, three-dimensional, tintype,
   transparency