function bp_activity_comments_user_avatars( $args = array() ) {

	$r = bp_parse_args( $args, array(
		'height' => false,
		'html'   => true,
		'type'   => 'thumb',
		'width'  => false,
	) );

	// Get the user IDs of everyone who has left a comment to the current activity item.
	$user_ids = bp_activity_get_comments_user_ids();
	$output   = array();
	$retval   = '';

	if ( ! empty( $user_ids ) ) {
		foreach ( (array) $user_ids as $user_id ) {

			// Skip an empty user ID.
			if ( empty( $user_id ) ) {
				continue;
			}

			// Get profile link for this user.
			$profile_link = bp_core_get_user_domain( $user_id );

			// Get avatar for this user.
			$image_html   = bp_core_fetch_avatar( array(
				'item_id' => $user_id,
				'height'  => $r['height'],
				'html'    => $r['html'],
				'type'    => $r['type'],
				'width'   => $r['width']
			) );

			// If user has link & avatar, add them to the output array.
			if ( ! empty( $profile_link ) && ! empty( $image_html ) ) {
				$output[] = sprintf( '<a href="%1$s">%2$s</a>', esc_url( $profile_link ), $image_html );
			}
		}

		// If output array is not empty, wrap everything in some list items.
		if ( ! empty( $output ) ) {
			$retval = '<li>' . implode( '</li><li>', $output ) . '</li>';
		}
	}

	/**
	 * Filters the list of linked avatars for users who have commented on the current activity item.
	 *
	 * @since 1.7.0
	 *
	 * @param string $retval HTML markup for the list of avatars.
	 * @param array  $r      Array of arguments used for each avatar.
	 * @param array  $output Array of each avatar found, before imploded into single string.
	 */
	echo apply_filters( 'bp_activity_comments_user_avatars', $retval, $r, $output );
}