Save Gravatars Locally and Display on WordPress Frontend

gravatars-locally.php

<?php
// Code begins here. It can be pasted into WPCode or CodeSnippets plugin or functions.php file of your child theme
function my_custom_gravatar($avatar, $id_or_email, $size, $default, $alt) {
    $email = '';
    if (is_numeric($id_or_email)) {
        $id = (int) $id_or_email;
        $user = get_userdata($id);
        if ($user) $email = $user->user_email;
    } elseif (is_object($id_or_email)) {
        if (!empty($id_or_email->user_id)) {
            $id = (int) $id_or_email->user_id;
            $user = get_userdata($id);
            if ($user) $email = $user->user_email;
        } elseif (!empty($id_or_email->comment_author_email)) {
            $email = $id_or_email->comment_author_email;
        }
    } else {
        $email = $id_or_email;
    }

    if ($email) {
        $local_avatar_folder = WP_CONTENT_DIR . '/avatars/';
        $local_avatar = $local_avatar_folder . md5(strtolower(trim($email))) . '.jpg';
        $local_avatar_url = content_url('/avatars/') . md5(strtolower(trim($email))) . '.jpg';

        if (!file_exists($local_avatar)) {
            $gravatar_url = 'https://www.gravatar.com/avatar/' . md5(strtolower(trim($email))) . '?s=' . $size;
            $image_data = file_get_contents($gravatar_url);

            if (!file_exists($local_avatar_folder)) {
                mkdir($local_avatar_folder, 0777, true);
            }

            file_put_contents($local_avatar, $image_data);
        }

        $avatar = "<img alt='{$alt}' src='{$local_avatar_url}' class='avatar avatar-{$size} photo' height='{$size}' width='{$size}' />";
    }

    return $avatar;
}

add_filter('get_avatar', 'my_custom_gravatar', 10, 5);