title: How do I copy an object from one S3 bucket to another only if its clone doesn't already exist in target
body: <p>I have been tasked with copying s3 objects from one bucket to another. The bucket contains millions of objects. The object should only be physically copied if either of two conditions are met.    </p>
  
  <p>The object does not exist in the target bucket or;
  The object in the source bucket has changed and no longer is identical to its counterpart in the destination bucket.   </p>
  
  <p>I am using the 1.5.3 version of the AWS SDK for .NET and I cannot change versions.    </p>