Long film showing in the pictures (4)
I believe the answer is:
epic
'long film' is the definition.
(I've seen this before)
'in the pictures' is the wordplay.
'in' says the answer is hidden in the clue.
'EPIC' is hidden within 'the pictures'.
'showing' acts as a link.
(Other definitions for epic that I've seen before include "A long poem or book with adventurous theme" , "imposing" , "Long poem telling of great events" , "Long poem set in nice picture" , "Heroic narrative verse" .)