collage vs photomontage

collage

noun
  • A picture made by sticking other pictures onto a surface. 

  • A composite object or collection (abstract or concrete) created by the assemblage of various media; especially for a work of art such as text, film, etc. 

  • The technique of producing a work of art of this kind. 

verb
  • To make into a collage. 

photomontage

noun
  • A composite image combining two or more photographs. 

  • The art of constructing such images. 

How often have the words collage and photomontage occurred in a corpus of books? (source: Google Ngram Viewer )