The pictures added skill to the author's material (7)
I believe the answer is:
artwork
'the author's material' is the definition.
The definition and answer can be both related to communication as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'the pictures added skill' is the wordplay.
'the pictures' becomes 'art'.
'added skill' becomes 'work' (I can't explain this - if you can you should believe this answer much more).
'art'+'work'='ARTWORK'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for artwork that I've seen before include "Illustrations and designs for printing" , "Illustrations in book" , "Illustrations prepared for a publication" , "Painting" , "Graphics" .)