Building a Cross platform Emoji System for Web/Android/iOS

I currently have a cross-platform app that runs as a

1. Website
2. Andorid App
3. iOS App

There is a chat system that can communicate with all 3 with Emoji, I have implemented the chat system with Emoji, using Image Links, and using HTML containers for Android and iOS.

However, I feel this way of implementing using images, is an overkill to the App loading time, and the Bandwidth consumption, Server gets overloaded with a number of requests (For each Emoji you get a call to the Webserver), plus even image-caching cost me due to the cloud-hosting ...etc

So i am looking for a Cross-platform way to implement an Emoji system with a much faster and universal way, So far i had a look at the

Using Unicode character approach,

which is the only thing i could find suitable with some problems, My question is there a better way to implement this? or Considering current Image link implementation what are the pros and cons of this?

How does apps like Facebook chat, skype, ...etc do this? is it based on the Unicode system or something else?

Any Insight or Advice into this is much appreciated.