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.
Lorena Cosba-could do this with students-a self portrait, and a contrasting image to show what's underneath. Note: Transformation in time peeling off effect layering the same face but in different time.
Take a mug shot style photo. Rip out the eyes rip out the mouth rip it in half shred it into as many pieces as possible and collage them do the thing in the pin out the face and stick it back upside down