Existe uma IMENSA coleção de artes 2D e 3D gratuitas e royalty free para uso em desenvolvimento e criação de jogos. Você não precisa pagar para baixá-las nem para usá-las.
Conheça e visite os 21 sites para fazer o download:
http://kenney.nl/assets
https://opengameart.org/
http://www.lostgarden.com/search/label/free%20game%20graphics
https://itch.io/game-assets/free
http://www.gameart2d.com/freebies.html
https://gameartpartners.com/downloads/totally-free-goodies/
http://www.graphic-buffet.com/freebies/
http://www.spriteland.com/sprites/
http://unluckystudio.com/
https://www.gameartguppy.com/product-category/free-game-art-sprites
https://openclipart.org/
http://www.reinerstilesets.de/2d-grafiken/2d-animals/
https://www.toptal.com/designers/subtlepatterns/
http://www.sharecg.com/
http://blogoscoped.com/archive/2006-08-08-n51.html
http://untamed.wild-refuge.net/rpgxp.php
https://crateboy.itch.io/crateboy-2007-2014
https://opengamegraphics.com/
http://www.glitchthegame.com/public-domain-game-art/
http://www.dumbmanex.com/bynd_freestuff.html
http://www.widgetworx.com/projects/sl.html