How are official EC2 images built?

From: Koichiro Iwao <meta_at_FreeBSD.org>
Date: Mon, 06 Mar 2023 02:15:33 UTC
Hi, 

Does anyone how offical EC2 images [1] are built?
I mean if the build script is public.  I would like to create private
custom images with some customization based on official image.

[1] https://aws.amazon.com/marketplace/seller-profile?id=92bb514d-02bc-49fd-9727-c474863f63da&ref=dtl_prodview-ukzmy5dzc6nbq

-- 
meta <meta@FreeBSD.org>