var md = require('markdown-it')({
  html: true,
  linkify: true,
  typography: true
}).use(require('markdown-it-imsize')); // <-- this use(package_name) is required

![test](image.png =100x200)

<p><img src="image.png" width="100" height="200"></p>

var md = require('markdown-it')({
  html: true,
  linkify: true,
  typography: true
}).use(require('markdown-it-imsize'), { autofill: true });