Tile artwork: FluffyStuff / riichi-mahjong-tiles
Source: https://github.com/FluffyStuff/riichi-mahjong-tiles
Upstream license statement (LICENSE.md):

This work is in the public domain. For more information, visit https://creativecommons.org/publicdomain/zero/1.0/.

This notice applies to the bundled files in tiles_img/, not to the application source code.
