They might be suing machines but a judge said the following:

When Warhol used Goldsmith’s photograph as a reference image, he “removed nearly all the photograph’s protectible [sic] elements.” Thus, Warhol did not violate the photograph’s copyright. Koetl explained his judgement through the perceived transformation of the image from Goldsmith to Warhol:

“The Prince Series works can reasonably be perceived to have transformed Prince from a vulnerable, uncomfortable person to an iconic, larger-than-life figure….The humanity Prince embodies in Goldsmith’s photograph is gone. Moreover, each Prince series work is immediately recognizable as a ‘Warhol’ rather than as a photograph of Prince — in the same way that Warhol’s famous representations of Marilyn Monroe and Mao are recognizable as ‘Warhols,’ not as realistic photographs of those persons.”

Machines (AI) don't copy reference images. They use bits and pieces (data) to create news ones.