So ...

We are going to use a handy plugin called WP User Avatar.

Here it is:

https://wordpress.org/plugins/wp-user-avatar/

This awesome plugin will allow you to ...

• upload your own default avatar in your WP User Avatar settings
• show the user’s Gravatar avatar or a default (defined) avatar if the user doesn’t have a WP User Avatar image
• disable Gravatar avatars and use only local avatars
• use the [avatar_upload] shortcode in order to add a standalone uploader to a front page or widget (which uploader is only visible to logged-in users)
• use the [avatar] shortcode in your posts/pages; these shortcodes will work with any theme, whether it has avatar support or not!
• allow Contributors and Subscribers to upload their own custom avatars
• limit upload file size and image dimensions for Contributors and Subscribers

It's a very small plugin (155 KB), but 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 ...

Now let's see how it works ...