Reciprocal airdrops without duplication

My partner airdropped photos from a trip to me - now I want to share my photos with him. (So we each will have a copy of each other's photos on our iphones.)

Because he airdropped to me first, my camera roll now contains both of our photos. I can't easily tell which are 'mine' and which are 'his'. How can I select only my photos to airdrop to him?