Photo turned up on the woman’s secret writing (6)
I believe the answer is:
cipher
'secret writing' is the definition.
(I've seen this in another clue)
'photo turned up on the woman's' is the wordplay.
'photo' becomes 'pic' (I've seen this before).
'turned up' says the letters should be written backwards.
'on' says to put letters next to each other.
'the woman' becomes 'her' (her refers to a woman).
'pic' written backwards gives 'cip'.
'cip'+'her'='CIPHER'
(Other definitions for cipher that I've seen before include "A message written in code" , "Person or thing of no importance, or the symbol 0" , "Nonentity" , "Secret code" , "Key to a code" .)