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]