Is this referring to the same type of "sticker" I hear about in iMessage? Because I still have no idea what those are about, but I hear people talking about them all the time.
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.