Constellation reflected in photograph (4)
I believe the answer is:
argo
'constellation' is the definition.
(I've seen this in another clue)
'reflected in photograph' is the wordplay.
'reflected' shows that the letters should be reversed in order (letters reflected back).
'in' says the answer is hidden in the clue.
'ogra' can be found hidden inside 'photograph'.
'ogra' back-to-front is 'ARGO'.
(Other definitions for argo that I've seen before include "Ancient ship" , "Old boat" , "Stars once recognised in the south" , "Transport to find the Golden Fleece" , "Ship Jason sailed to find the Golden Fleece" .)