photo credit vs mention

photo credit and mention both are nouns.

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

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

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

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

photo credit (noun)	mention (noun)
a note acknowledging the source of a published photograph	an official recognition of merit
	a remark that calls attention to something or someone
	a short note recognizing a source of information or of a quoted passage