留念可译为 as a memento （变体拼写 momento）, as a souvenir, as a keepsake 最佳翻译要看语境， 比如 合影留念 have a group photo taken to mark the occasion; 照相留念 have a photo taken as a memento; 赠物留念 to give a present as a keepsake.
不同的语境可以有不同的说法用法 比如接受礼物作为留念 你可以说 accept/keep it (as a souvenir作为纪念): 合影留念have a group photo taken to (mark the occasion留念v); 照相留念have a photo taken （as a memento作为纪念）;本回答被网友采纳