Picture Perfect

(oops, missed the last challenge! Trying again on this one)

It's not big,
A grandfather clock,
It's not small,
A desk clock,
It's not on a chain,
A pocket clock,
It's not on a wall,
A mantel clock,
It's not electric,
An alarm clock,
It's not sunlit,
A sundial,
It's not musical,
A cuckoo clock,
It's not constantly ticking,
A pendulum clock,
It shows a time,
Yet never changes what it shows,
I wonder why it does this,
Why it never seems to age,
What is wrong with my clock?
Is it broken?
But upon closer inspection,
I see it for what it truly is.
My beautiful clock is simply a portrait.
How sad that is to know.