Puzzle that's new in processing image (6)
I believe the answer is:
enigma
'puzzle' is the definition.
(thesaurus)
'new in processing image' is the wordplay.
'new' becomes 'n'.
'in' indicates putting letters inside.
'processing' is an anagram indicator.
'image' with letters rearranged gives 'eigma'.
'n' going within 'eigma' is 'ENIGMA'.
'that's' acts as a link.
(Other definitions for enigma that I've seen before include "Puzzle of gamine (6)," , "WW2 code" , "Something mysterious and puzzling" , "Mysterious or puzzling thing" , "Title of Elgar's set of variations" .)