WPAvatarreplace.php

add_filter('get_avatar_url', 'wpse_avatar_or_gravatar', 10, 3);
function wpse_avatar_or_gravatar($url, $email, $args) {
  //  Manually edit the /wp-admin/includes/class-wp-users-list-table.php (439) and /wp-includes/admin-bar.php to show avatar using email

    $path = sprintf('/home/asdasd/public_html/wp-content/images/users/%s.jpg',
                md5(strtolower(trim($email . "scripto")))
            );

    $url = sprintf('%s/images/users/%s.jpg',
                "//www.asd.com/wp-content",
                md5(strtolower(trim($email . "scripto")))
            );

    if (file_exists($path)) {
        // image exists, return url
        $url = sprintf('//www.asd.com/wp-content/images/users/%s.jpg',
                md5(strtolower(trim($email . "scripto")))
            );
    }
    else {
        // image does not exist, return default avatar
        $url = "https://0.gravatar.com/avatar/" . md5( strtolower( trim( $email ) ) ) . "?s=64&d=identicon&f=y&r=g";              
    }

    return $url;
}