A picture forged: active safety measure (10)
I believe the answer is:
precaution
'safety measure' is the definition.
(I've seen this before)
'a picture forged active' is the wordplay.
'forged' indicates anagramming the letters.
'active' becomes 'on' (I've seen this in other clues).
'a'+'picture'='apicture'
'apicture' with letters rearranged gives 'precauti'.
'precauti'+'on'='PRECAUTION'
(Other definitions for precaution that I've seen before include "Safety measure" , "Measure taken in case it proves to be necessary" , "foresight" , "Advance measure taken against an undesirable development" , "Safeguard" .)