I'm not criticizing you when you say that you need stickers, but please help me understand: how do you rely on stickers to communicate?

I can understand them being a nice UI/UX feature that makes the app more fun, but I cannot possibly imagine that people actually rely on stickers to communicate.

Maybe you mean something different and I'm misunderstanding you?

Not me as an individual, but various communities I'm in contact with have stickers ingrained into their culture and social norms. People collect up to hundreds of stickers for different situations, make their own based on shared iconography, and some even have custom stickers commissioned from artists, of themselves, of characters they've created, etc. For groups that are really invested in stickers, migrating to an app which lacks them would significantly alter their dynamics.

You don't understand. I live for stickers on Telegram. It's an essential part of communication for millions. This is not a joke. Especially in Asia

To succinctly convey emotions, opinions, viewpoints, "feels". To simply have a non-verbal vocabulary, to have a different quality to certain parts of the communication, to signify a different quality of seriousness/playfulness/feeling.

It's the new emoticon. :-)

I'm curious, are they used anything like memes that you can easily send more than once?

Not sure what you mean by "like memes". They are just funny images with thousands of variations that you can send. If you're going to sleep - send something cute that shows it.

Some examples http://www.line-stickers.com/

The only thing I could see that would potentially top this would be talking animated emoji....The feces one comes to mind specifically

It it talks, it takes too much time to parse, and it becomes too specific.

Pictures, maybe with a max 0.5 sec animation are okay, and no sound. (At least that's my hunch.)

So basically emojis?

Sure, if emojis could be infinitely extended with arbitrary images and were sent as their own messages instead of being embedded inline with other text. Replying to another message with a sticker also fills the role played by reactions on Facebook Messenger.

I use some of them to communicate moods, or recurring ideas that are bothersome to enunciate over text.

E.g. these:

https://stickers.acidodivertido.com/wp-content/uploads/2017/...

If you pass links to known sticker images, and the recipient has to retrieve them by means outside the Signal protocol, that reduces security. An observer can detect when a receiver fetches a sticker image, and they can tell which one. For example, noting that a message has forced the loading of collection "Gay"[1] provides much useful information to an observer.

[1] http://chpic.su/en/stickers/Gayer/

So send them entirely inline. Sending a sticker is not fundamentally different from sending an image that isn't called a "sticker".

Having to send stickers every time ups the overhead. Also, if stickers are well known variable length files, it may be possible to make good guesses about which stickers are attached.

You could negotiate sticker sending by hash: the first message only contains the hash value, if the recipient already has that sticker stored, it can be displayed immediately. Otherwise the full data can be requested.

EDIT: That scheme can be used to probe whether or not someone already has a specific sticker stored, so it might have to be separated per-contact to avoid leakage.