Maybe copyright pictures, dividing stock in three (10)
I believe the answer is:
tripartite
'maybe copyright pictures' is the definition.
I can't tell whether this defines the answer.
'dividing stock in three' is the wordplay.
'dividing' indicates putting letters inside (inserted letters divide the word).
'stock' becomes 'trite' (I've seen this before).
'in three' becomes 'parti' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'trite' placed around 'parti' is 'TRIPARTITE'.
Can you help me to learn more?
(Other definitions for tripartite that I've seen before include "in several sections?" , "such as a three-piece suit" , "Like Henry VI" , "after a couple of cuts" , "in several pieces" .)