I am looking at these docs:
https://dev.twitter.com/web/tweet-button
I tried a couple of their examples, like so:
<a class="twitter-share-button" href="https://twitter.com/intent/tweet">
Tweet
</a>
However, this only displays the text "Tweet" without an image. I assume an image is supposed to be included, so what am I missing here?
You are missing the javascript file.
<script type="text/javascript" async src="https://platform.twitter.com/widgets.js"></script>
<a class="twitter-share-button" href="https://twitter.com/intent/tweet">
Tweet
</a>