"Why do people keep photographs? (...) that's reason No. 1. Vanity. Now reason No. 2. Sentiment. (...) And there is, probably a third category. No vanity, not sentiment, not love - perhaps hate - what do you say?"
"Hate?"
"Yes. To keep a desire for revenge alive. Someone who has injured you - you might keep a photograph to remind you, might you not?"

in Mrs. McGinty's Dead, by Agatha Christie.