Yep, once again, everything starts with a handy plugin ... called WP Image Zoom.

Here it is:

https://wordpress.org/plugins/wp-image-zoooom/

Before anything else, let's see the speed test.

Here's my result before installing the plugin ...

... and here are the results after installing and activating the plugin:

I'd say that 90 ms is an acceptable price for this cool and important feature ...

With that having said, let's see how it works ...