Poor Garth suffering negative image (9)

I believe the answer is:

rotograph

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'negative image' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'poor garth suffering' is the wordplay.
'suffering' indicates anagramming the letters.
'poor'+'garth'='poorgarth'
'poorgarth' anagrammed gives 'ROTOGRAPH'.

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(Another definition for rotograph that I've seen is " Reverse picture".)

I've seen this clue in The Guardian.

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