WordPress at a glance
filter is not described

get_avatar_url filter-hook . WP 4.2.0

Filters the avatar URL.

Usage

add_filter( 'get_avatar_url', 'filter_function_name_4927', 10, 3 );
function filter_function_name_4927( $url, $id_or_email, $args ){
	// filter...

	return $url;
}
$url(string)
The URL of the avatar.
$id_or_email(mixed)
The Gravatar to retrieve. Accepts a user_id, gravatar md5 hash, user email, WP_User object, WP_Post object, or WP_Comment object.
$args(array)
Arguments passed to get_avatar_data(), after processing.

Where the hook is called

get_avatar_data()
wp-includes/link-template.php 3972
$args['url'] = apply_filters( 'get_avatar_url', $url, $id_or_email, $args );

Where the hook is used (in WP core)

Does not used.