Photo captures an outbreak of terror (5)
I believe the answer is:
panic
'outbreak of terror' is the definition.
(panic is a feeling of terror)
'photo captures an' is the wordplay.
'photo' becomes 'pic' (short for picture).
'captures' indicates putting letters inside.
'pic' enclosing 'an' is 'PANIC'.
(Other definitions for panic that I've seen before include "general alarm" , "Sudden overpowering anxiety" , "Great consternation" , "Grass" , "Sudden alarm" .)