Rocket.Chat/app/ui-message/client/blocks/ImageBlock.html

<!-- {
	"type": "image",
	"title": {
		"type": "plain_text",
		"text": "Example Image",
		"emoji": true
	},
	"image_url": "https://api.slack.com/img/blocks/bkb_template_images/goldengate.png",
	"alt_text": "Example Image"
}, -->

<template name="ImageBlock" arguments="title image_url  alt_text">
	<fieldset class="block-kit-debug">
		<legend>ImageBlock</legend>
		<div>{{>TextBlock title}}</div>
		<img src={{image_url}} alt={{alt_text}}/>
	</fieldset>
</template>