iOS provides a richer way to express feelings via iMessages using various stickers. And most interestingly these stickers are not limited, one can build their own stickers too and submit it to iTunes stores like other apps.
Here I’m going to tell you how one can create their own stickers.

Basic Requirements:

1. Supported Image formats: PNG, JPEG, GIF or APNG.
2. Maximum size of images is 500KB
3. You need various size of app icon for your sticker app.
4. Xcode8.0 or later.

Steps to create Sticker pack application:

1. Start Creating the app by launching Xcode and click “New Project” 
2. Select iOS platform and application template as “Sticker Pack Application”.
3. Fill your project details like name and bundle identifiers etc.
4. You’ll find a file named “Stickers.xcstickers” this is the file where we are going to drag and drop our stickers/items.
5. Select the folder named “Sticker Pack” and add images by dropping items to it(easiest way of adding images to folder). You can add various formats of images like PNG, JPEG, GIF or APNG. This means you can add animated images to stickers as well. Make sure that maximum size of images is no more than 500KB
6. You can simply drag and drop GIF and APNG to the folder like other images.
7. If you want to add individual frames of an animated image then select “New Sticker Sequence” from editor menu.
8. Once you are done with the above step drag all sequence of image to new sticker sequence you created above.
9. You can control various properties of animated images you created at #6 & #7 like animation duration, repetitions, frame rate etc.
10. Like other Xcode application sticker pack also needs an app icon. Select “Message App iCon” option from list and provide icons of all different size. 

That’s all and you are done!! :)

Now select the device type and run the application from product menu. 

iOS simulator opens and Messages will launch and you can see your Stickers. Now if you tap on stickers it will put the same on textfield where you can send it to any.