Pictures of mirage shimmering before day’s end (7)
I believe the answer is:
imagery
'pictures' is the definition.
(I've seen this in another clue)
'mirage shimmering before day's end' is the wordplay.
'shimmering' is an anagram indicator (letters shimmer or shake around).
'before' says to put letters next to each other.
'end' suggests the final letters.
The final letter of 'day' is 'y'.
'mirage' anagrammed gives 'imager'.
'imager'+'y'='IMAGERY'
'of' is the link.
(Other definitions for imagery that I've seen before include "I'm gayer due to mental pictures" , "Figurative language, eg, in poem" , "Mental pictures - I am grey (anag)" , "statues etc." , "Visual symbolism" .)