The artist retains all rights under the Copyright Act of 1976 (17 USC Section 101) as the sole author of the work for the duration of the copyright. The duration of copyright in the United States is currently the life of the author, plus 70 years.
Title to the artwork passes to the client or commissioning agency/organization upon their written acceptance of and payment for the work, but copyright belongs to and remains with the artist. In other words, although the client may "own" the work of art, the artist who created the work owns the copyright, including all ways in which that artwork is represented (photos, video, ads, logos, branding), other than in situ (on-site documentation photos). Artists may wish to register their copyright with the federal government. For more information on copyright, refer to Public Art Network's Best Practices Guidelines.
One of the results of the Visual Artist Rights Act (VARA) has been the establishment of a more formal and prolonged relationship between the artist and the commissioning agency. This relationship is typically further enumerated in the contract for the commission.
When there is an issue with an artwork, such as damage or changes to its site or context, then the owner of that artwork should communicate directly with the artist. This benefits the owner and the artist, both of whom have a vested interest in the well-being of the artwork. As a matter of best practices, if an artwork needs to be removed, then the artist should be given the first right to regain ownership, remove the artwork, or disclaim authorship, even if VARA rights have previously been waived.