1860, a colloquial shortening of photograph. The verb is by 1865, from the noun. Photo-finish, of a race that ends with two or more competitors crossing the finishing line at nearly the same time (so a photograph taken at the finish line at the moment of crossing is the only way to determine who won) is attested from 1936. Photo opportunity "arranged opportunity to take a photograph of a notable person or event" is from 1974, said to be a coinage of the Nixon Administration.
"technique of producing a composite or consecutive whole from fragments of pictures, text, music, etc.," 1929, from French montage "a mounting," from Old French monter "to go up, mount" (see mount (v.)). Originally a term in cinematography.
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<a href="https://www.etymonline.com/word/photomontage">Etymology of photomontage by etymonline</a>
Harper, D. (n.d.). Etymology of photomontage. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/photomontage