A crack in the picture (4)
I believe the answer is:
shot
This clue is a double definition.
'a crack' is the first definition.
(I know this)
'picture' is the second definition.
(I know that shot is a type of picture)
'in the' is the link.
(Other definitions for shot that I've seen before include "Crack" , "Small drink of spirits" , "Try -- ammunition" , "Zoomed" , "Sent a bullet" .)