Rocket.Chat allows you to add custom emoji files that can be used within Rocket.Chat .
Go to the Administration tab
Select Custom Emoji
Click the + on the top right
Enter a name for your custom emoji
Enter an alias for your custom emoji
Browse and choose a image file in PNG or JPEG format
To use a custom emoji that you've added either click the emoji icon on the message input and search for your custom emoji by its name or enter
:custom_emoji_alias: in the message box to directly add the emoji.
Search and click on the custom emoji you want to delete in the
Custom Emoji section under the
Press Delete or Edit to delete or update the selected emoji, respectively.