That looks kinda similar, except it seems iMessage allows you to slap stickers in arbitrary positions on top of other messages, whereas the implementations I'm

That looks kinda similar, except it seems iMessage allows you to slap stickers in arbitrary positions on top of other messages, whereas the implementations I'm thinking of just treat a sticker as its own message. Also Apple has some sort of sticker store and approval process, whereas on Telegram for example anyone can add their own image files for use as stickers.