One million years in pictures (6)
I believe the answer is:
images
'pictures' is the definition.
('image' can be a synonym of 'picture')
'one million years' is the wordplay.
'one million' becomes 'im' (I've seen this in other clues).
'years' becomes 'ages' (I've seen this before).
'im'+'ages'='IMAGES'
'in' acts as a link.
(Other definitions for images that I've seen before include "Pictures or photos" , "Reflections in a mirror" , "Likenesses, representations" , "Visual or mental representations" , "These doubles could be spitting" .)