I truly dislike Getty due to the fact that they use an ENORMOUS number of public domain images, and try to pass themselves off as having ownership rights. It is selfish and disgusting. And there should be a way to punish entities who do this. (You might be surprised how many places do this, including taxpayer funded museums here in the USA...)
However, the Library of Congress page of "Carol M. Highsmith - Rights and Restrictions Information" at:
"Carol M. Highsmith's photographs are in the public domain."
The article that appears on PDNPULSE:
"Highsmith says she never abandoned her copyrights to the images. She says the Library of Congress had agreed to notify users of the images that she is the author, and that users must credit her."
If the images are public domain, she did not retain the right to enforce accreditation.
What she is describing would be equivalent to a Creative Commons Attribution License.
Part of the reason for a cc-by license is to stop greedy folks from reselling and trying to "own" what would otherwise be public domain works.
Of course, those of us who work at organizing, editing and adding our own works to the public domain on sites such as my wpclipart.com,
cannot touch anything with a cc-by license.
What would be much better is if there was a legal mechanism to punish people for falsely claiming rights/ownership of images.
Without it, greedy companies/entities are continually narrowing what is available in the public domain.