The Collaborative International Dictionary of English v.0.48:

collage \collage\ n.
   1. any picture made by sticking together pieces of paper or
      photographs, especially in unusual or surprising ways.

   Syn: montage.
        [WordNet 1.5]

   2. the technique of producing a work of art that is a
      collage[1].
      [PJC]

   3. any composite object, whether abstract or concrete,
      created by assembling components of varied types.
      [PJC]

   4. (Cinema) a film having scenes of different types or from
      different locations displayed in rapid succession without
      transitions.
      [PJC]

WordNet (r) 3.0 (2006):

collage
    n 1: a paste-up made by sticking together pieces of paper or
         photographs to form an artistic image; "he used his
         computer to make a collage of pictures superimposed on a
         map" [syn: collage, montage]
    2: any collection of diverse things; "a collage of memories"

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "collage":
   abstract, abstraction, altarpiece, block print, color print, copy,
   cyclorama, daub, diptych, engraving, fresco, icon, illumination,
   illustration, image, likeness, miniature, montage, mosaic, mural,
   panorama, photograph, picture, print, representation, reproduction,
   stained glass window, stencil, still life, tableau, tapestry,
   triptych, wall painting