So ...

We are going to use a handy plugin called Pinterest Pin It Button For Images.

Here it is:

https://wordpress.org/plugins/pinterest-pin-it-button-for-im...

Note: you'll see the usual warning message saying that the plugin hasn’t been tested with the latest major releases of Wordpress ... Ignore it ... I've tested the plugin on Wordpress 5.1 and works fine.

It's a medium-size plugin (290 KB), so let's see the usual speed tests ...

Here are my results before installing the plugin ...

... and the result after installing and activating the plugin:

No more comments needed ...

So, let's see how it works ...