What is the difference between using aws_cdk.aws_ecs.EcrImage and aws_cdk.aws_ecs.ContainerImage to create instances using CDK?
Not much. ecs.EcrImage specifically represents an Amazon ECR Registry image. It extends ecs.ContainerImage construct, adding only an imageName property.
ContainerImage has static methods to return non-ECR (e.g. DockerHub) images. Perhaps confusingly, EcrImage inherits these factory methods as well.