The best alternatives to Covatar are Avatar, Diversity Avatars, and Avatar SDK. If these 3 options don't work for you, we've listed a few more alternatives below.
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The Diversity Avatars collection is an exploration of the beauty and diversity of people and cultures around the world, including all walks of life, religions, and nationalities. UPDATE April 5, 2019 : 750 avatars - https://diversityavatars.com/the-avatars