Take a look at nostr:npub1r6d0rcg8d0n0x7w5m4w3cx96jdgar3f9l48zqndjuq7hhcg282ysv57ww0 previous contests, last weekends for example, the memes are submitted under the note, you can read the rules in the bottom nostr:note1vpusxq243awrnp4w75a6pnc7j3rpnvheg9uagkcpwjk2cpeq86hsa4nxx9