Supposed to have to stand for photo (4)
I believe the answer is:
pose
'stand for photo' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'supposed to have' is the wordplay.
'to have' indicates the answer is hidden within the clue.
'POSE' can be found hidden inside 'supposed'.
'to' is the link.
Can you help me to learn more?
(Other definitions for pose that I've seen before include "'Present, a problem say (4)'" , "Affectation" , "Arrange, model" , "Attitudinise" , "Present (problem), sit" .)