Xjyuk

Recent news events in the US have resulted in many headlines about "nude photos of young women" and variations.

Obviously it's the women who are nude, not the photos, so why does this phrasing persist? Is it an idiom, or does it just flow better, or is it some other nuance of usage that I haven't seen in other situations?

nude ADJECTIVE

...

1.1 [attributive] Depicting or performed by naked people.
‘she won't do any nude scenes’
Lexico

It’s a way to to refer to photos with nude subjects. As you can see from Ngram this expression took off from the ‘60s/70s when pictures portraying nude people, generally women, started to become popular, as in earlier expression used referring to paintings

Nude:

(of a photograph, painting, statue, etc.) being or prominently displaying a representation of the nude human figure.

(Dictionary.com)

Nude photos is a noun phrase that has become idiomatic and manifests in slang such as "nudies" or simply "nudes". The phrase "nude photos of X" does indeed seem like a retro-construction. This phrasing is also more euphemistic or neutral, perhaps, since as you mentioned, technically, it would be "X" who is nude, but "X" is not the grammatical subject (it is instead within the prepositional "of X").

@user240918 and @GEdgar also make good points.

Note Webster:

nude (adj) bare, naked, nude, bald, barren mean deprived of naturally or conventionally appropriate covering. ... nude applies especially to the unclothed human figure.

Collocations modifying photo often don't refer to the photo as a physical object. They instead refer to the subject of the photo, or what's depicted in the image.

To demonstrate this, here are the most common collocations for ____ photo according to the Corpus of Contemporary American English. I have bolded the ones that describe the image (source, subject, or whatever) and italicized the ones that describe a property of the physical photograph. Other results are left unchanged. Numbers describe frequency within the corpus.

• these (434)


• 
  family (379)


• 
  two (316)


• take (243)


• 
  color (234)


• 
  AP (225)


• those (222)


• taking (180)


• 
  digital (168)


• 
  old (160)


• 
  scene (147)


• 
  three (135)


• 
  nude (129)


• 
  framed (124)


• 
  satellite (122)


• 
  black-and-white (113)


• took (112)


• 
  aerial (91)


• 
  four (87)


• 
  five (84)


• snapping (82)


• 
  wedding (63)

Out of these results, a family photo is understood to be a photo of a family, just as a wedding photo is understood to be a photo of a wedding. Similarly, English has other constructions, like nude photo. The same positioning can also describe provenance (AP photo, satellite photo, aerial photo), quality of photo (black-and-white photo, color photo), physical status (framed photo, digital photo), and so on.

Hearers understand nude photo to refer to what's in the photo because of established usage. Also, the idea of a photo in the "nude" does not make much sense, so the physical interpretation of the object is unlikely. Many media objects have this quality; a ___ book can refer to either the physical object (big book, hardcover book) or to a quality of the text inside (a sad book, a scholarly book). A bit of logic and some arbitrary usage rules determine how people interpret collocations involving media objects.