Telegram is fantastic. I could go on and on but I don't want this to sound like an advert for em. Just go check out the FAQ.
Anywho, telegram makes stickers and sticker packs but they give the freedom to create custom sticker packs to all users. They're really easy to make and they've got a bot that take you through the process.
I've created a few sticker packs now but I am most proud of one created with the 'Earl of Lemongrab' from the tv show "Adventure Time." I've got a loink to it down below. I created the sticker pack by taking screenshots of the show, removing the background and cleaning them up, and then editing certain aspects of some of them to make the stickers really quite good. I did all the editing using GIMP, so I suppose I'll leave a loink for that as well.
I'm currently working on a sticker pack using the characters from a youtube animator called "Cas van de Pol." Specifically the character Maxmoefoe, the goblin, and Grömpie.
Telegram FAQ: start at telegram basics for features
Sticker Bot: Custom stickers, baby!
Lemongrab Stickers: LEMONY JUICES
MaxMoeFoe/Cas Stickers: Ik ben het Grömpie!
GIMP, Open Source Photo Editor: GIMP

