An Amazon Machine Image (AMI) is a template that contains the software configuration ( operating system, application server, and applications) required to launch your instance.
AMI provides the information required to launch an instance. At launching an instance must be specified as an AMI.
A config rule that checks whether the Amazon Machine Images are not publicly accessible. The rule is NON_COMPLIANT if one or more Amazon Machine Images are publicly accessible.
Amazon EC2 enables you to share your AMIs with other AWS accounts. You can allow all AWS accounts to launch the AMI (make the AMI public), or only allow a few specific accounts to launch the AMI (see Sharing an AMI with Specific AWS Accounts). You are not billed when your AMI is launched by other AWS accounts; only the accounts launching the AMI are billed.
By default, AMIs are private.
If you want to revoke changes that mean you want to set image as public, follow the implementation steps and choose public.