Picture of a biscuit (4)
I believe the answer is:
snap
This clue is a double definition.
'picture' is the first definition.
(I know that snap is a type of picture)
'a biscuit' is the second definition.
(I know that snap is a type of biscuit)
'of' acts as a link.
(Other definitions for snap that I've seen before include "Spell of cold weather and card game" , "you may take on holiday" , "Break like simple card game" , "Speak in a sharp angry tone" , "Sudden break" .)