For lazy loading images use a plugin called Lazyload
In documentation is described how to fix it, even mixin Sass wrote.
Padding Bottom = (Image Height / Image Width) * 100%
padding-bottom: 66.67%; /* You define this doing height / width * 100% */
But I have different height of the image. How do I calculate height? The website is built on Wordpress, can code php to intercept sizes, and add inline. You can implement it in Js or other method?