cburnett chess piece set by Colin M.L. Burnett (https://en.wikipedia.org/wiki/User:Cburnett).
Source: https://github.com/lichess-org/lila/tree/master/public/piece/cburnett
License: GPLv2+ (https://www.gnu.org/licenses/gpl-2.0.txt), as listed in lila's COPYING.md.