Copyright does not protect you from the images being further edited by the client, even if you ask then not to. If you have a contract that they have signed stating that they can not further edit the photos, then that will be legally binding if you specify precisely what constitutes editing... just for legal clarity... but this is nothing to do with copyright. These are your moral rights, but you can not enforce moral rights unless you have asserted them in writing, usually by including the words "All moral rights asserted" in the contract, license to use or on the image itself.
You had a separate contract enforcing this and you are not really affected, but so many people assume that copyright protects the client further altering the images... and it just doesn't. You have to assert your moral rights, or as in your case, you produced a contract stipulating your requirements.
Copyright doesn't stop people editing your images, not does it grant you rights to attribution.