A picture of placidity (5)

I believe the answer is:

still

I'm a little stuck... Click here to teach me more about this clue!

'a picture' is the definition.
(still is a kind of picture)

I don't understand how the remainder of the clue works.

(Other definitions for still that I've seen before include "Silence" , "Tranquil" , "source of spirits" , "Immobile" , "Not going anywhere" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app