Policeman's a poser in pictures (5)
I believe the answer is:
rebus
This clue is a double definition.
'policeman's' is the first definition.
(fictional detective John Rebus)
'a poser in pictures' is the second definition.
(picture-based puzzle)
(Other definitions for rebus that I've seen before include "Visual type of word puzzle" , "Puzzling device" , "Pun picture puzzle" , "Enigmatic representation" , "Word puzzle involving pictures" .)