photomontage vs montage

photomontage and montage both are nouns.

Word	Noun	Adjective	Verb	Adverb
photomontage	Yes	No	No	No
montage	Yes	No	No	No

As nouns, montage is a hypernym of photomontage; that is, montage is a word with a broader meaning than photomontage:

photomontage: a montage that uses photographic images
montage: a paste-up made by sticking together pieces of paper or photographs to form an artistic image

Other hypernyms of photomontage include collage.

photomontage (noun)	montage (noun)
a montage that uses photographic images	a paste-up made by sticking together pieces of paper or photographs to form an artistic image