Copyright laws for paintings after they are sold can vary, but in most circumstances, the artist retains ownership of the copyright, even after the artwork changes hands. This means that the buyer does not automatically acquire the right to reproduce the painting as cards, prints, posters, or on t-shirts. However, there are a few exceptions to this rule. If the artist specifically signed over their copyright to the buyer, or if the artwork was created as a work for hire, the buyer may own the copyright. Additionally, if the copyright has expired, the buyer may be able to reproduce the artwork without infringing on the artist's rights.
It's important to note that the rights around artwork are not always straightforward. For example, under the Visual Artist Rights Act of 1990 (VARA), artists retain certain powers of attribution and disavowal long after the ownership of the actual tangible work of art is in the possession of a collector or institution. Additionally, if a buyer copies a painting and sells it as a derivative work, they may be liable for copyright infringement if the work is not transformative. This could result in damages being awarded to the artist, as well as potential criminal charges and damage to their reputation.