stock photograph vs photo

stock photograph and photo both are nouns.

Word	Noun	Adjective	Verb	Adverb
stock photograph	Yes	No	No	No
photo	Yes	No	No	No

As nouns, photo is a hypernym of stock photograph; that is, photo is a word with a broader meaning than stock photograph:

stock photograph: an existing photograph licensed for a specific use
photo: a representation of a person or scene in the form of a print or transparent slide or in digital format

Other hypernyms of stock photograph include exposure, photograph, pic, picture.

stock photograph (noun)	photo (noun)
an existing photograph licensed for a specific use	a representation of a person or scene in the form of a print or transparent slide or in digital format