16 pixels by 16 pixels is a common resolution for assets matching a low-res pixel art aesthetic. Although the assets may not be specifically 16x16, they are designed to work in a graphical setting where objects are around that size.
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Pretty sure everything is indie on itch.io but just in case you want something extra indie.
For that old school look and feel.
Explore game assets tagged 16x16, Indie and Retro on itch.io · Sell your game assets on itch.io to have them show up here.
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