Human face made of several different people, artistic concept collage by Zurijeta, via ShutterStock
This example of photomontage works well because it is visually interesting and has a lot of contrast. The photo of the woman is in black and white while the photo of the plant is shown in color this contrast makes the image stand out more.
Brno Del Zou Take multiple photos, cut them into different sized fragments and reassemble them in odd places that still work.
Self portrait ideas Mapping 2013 on Behance Use a process like this for "identity/self-concept" activity about skin color/shade/tone/palette. Put vertical photo strip of every child together on a couple images to make a collective face.
Joe Webb, Stirring Up A Storm, Original Collage Courtesy of the Saatchi Gallery, London