in each category, from top to bottom: more to less likely to be under an open license
still image
https://commons.wikimedia.org/wiki/Category:Images
https://opengameart.org/art-search-advanced?field_art_type_tid%5B%5D=9
https://opengameart.org/art-search-advanced?field_art_type_tid%5B%5D=14
https://opengameart.org/art-search-advanced?field_art_type_tid%5B%5D=7273
https://archive.org/details/image
https://textures.neocities.org/
https://www.newgrounds.com/art
https://www.textures-resource.com/...
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