How to add more header images to default

If you are talking about TwnetyTen theme….

Do a search on ThirtyTen which is a template based on the standard TwentyTen but with a lot of custimisations. One of them is addign a few images to the standard ones.
The website has a good description of how to do this and you can also donwload the template and see how it is done, check functions.php

This link helped me out on the same subject:
https://www.wpbeginner.com/wp-themes/adding-additional-default-headers-to-the-wordpress-twenty-ten-theme/