IAM to prevent launching Public AMIs

You can leverage Condition operator in IAM JSON policy elements Eg. Boolean conditions enable the creation of Condition elements that limit access by comparing a key to either "true" or "false."

{
            "Sid": "DenyLaunchingPublicAMI",
            "Effect": "Deny",
            "Action": "ec2:RunInstances",
            "Resource": "arn:aws:ec2:<region>::image/ami-*",
            "Condition": {
                "Bool": {
                    "ec2:Public": "true"
                }
 }

Document:

• https://docs.aws.amazon.com/IAM/latest/UserGuide/reference_policies_elements_condition_operators.html#Conditions_Boolean