Final plates put on to nullify about four reversed images (9)
I believe the answer is:
negatives
'images' is the definition.
(I know this)
'final plates put on to nullify about four' is the wordplay.
'final' suggests the final letters.
'put on' means one lot of letters go next to another.
'to nullify' becomes 'negate' (I've seen this in another clue).
'about' means one lot of letters goes inside another.
'four' becomes 'IV' (Roman numerals).
The last letter of 'plates' is 's'.
'negate' placed around 'iv' is 'negative'.
's' put after 'negative' is 'NEGATIVES'.
'reversed' is the link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for negatives that I've seen before include "Original shots" , "Reverse photos?" .)