Disable Gravatar and Use Local Fallback Avatar

<?php
if ( ! function_exists( 'scseed_disable_gravatar' ) ) {
    function scseed_disable_gravatar( $args, $id_or_email ) {
        // Serve a local fallback image instead of Gravatar.
        $args['url']          = get_stylesheet_directory_uri() . '/images/default-avatar.png';
        $args['found_avatar'] = true;
        return $args;
    }
    add_filter( 'pre_get_avatar_data', 'scseed_disable_gravatar', 10, 2 );
}