photo credit vs citation

photo credit and citation both are nouns.

Word	Noun	Adjective	Verb	Adverb
photo credit	Yes	No	No	No
citation	Yes	No	No	No

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

photo credit: a note acknowledging the source of a published photograph
citation: a short note recognizing a source of information or of a quoted passage

Other hypernyms of photo credit include acknowledgment, cite, credit, mention, quotation, reference.

photo credit (noun)	citation (noun)
a note acknowledging the source of a published photograph	an official award (as for bravery or service) usually given as formal public statement
	a short note recognizing a source of information or of a quoted passage
	a summons that commands the appearance of a party at a proceeding
	a passage or expression that is quoted or cited
	(law) the act of citing (as of spoken words or written passages or legal precedents etc.)