Addition to book — a page to finish in pictures (8)
I believe the answer is:
appendix
'addition' is the definition.
(thesaurus)
'book a page to finish in pictures' is the wordplay.
'book a page' becomes 'ap' (I can't justify this - if you can you should believe this answer much more).
'to finish' becomes 'end' (come to an end).
'in' indicates putting letters inside.
'pictures' becomes 'pix' (short for pictures).
'end' inserted inside 'pix' is 'pendix'.
'ap'+'pendix'='APPENDIX'
'to' acts as a link.
Can you help me to learn more?
(Other definitions for appendix that I've seen before include "Addition to a book" , "Extra bit" , "part of book" , "has no known use" , "It's useless in the body, but useful in a book" .)