The script I linked to you does this for you, and it explains how to use it. Specifically, you’d do something like this:
<img data-twitch-channel="riotgames" data-offline-image="riotgames.png" data-online-image="riotgames-live.png">
<img data-twitch-channel="lirik" data-offline-image="lirik.png" data-online-image="lirik-live.png">
<img data-twitch-channel="beyondthesummit" data-offline-image="beyondthesummit.png" data-online-image="beyondthesummit-live.png">
<script src="https://code.jquery.com/jquery-1.11.1.min.js"></script>
<script src="https://cdn.rawgit.com/Fugiman/Twitch-Channel-Status/1d74252edf89110507cbf3088f9c3eaa38fac9d3/twitch-channel-status.min.js"></script>
Does that make it clear?