Analysis
This decision strengthened the rights of those who wish to make use of works that have passed into the public domain. If this lawsuit had been decided the other way, claims based on trademark, or even based on moral rights such as attribution of authorship, could have been used to make it impractical for anyone to use works in the public domain as intended by Article One of the United States Constitution.
Dastar might have been able to avoid this legal attack entirely if they had credited the original authors. However, as Scalia noted in the opinion, this would have put them in a bind: crediting the original authors might have implied their sponsorship or approval, which could have exposed Dastar to other lawsuits, unless the credit had been carefully worded.
Congress has repeatedly extended the term of U.S. copyrights, with legislation such as the Sonny Bono Copyright Term Extension Act.
Read more about this topic: Dastar Corp. V. Twentieth Century Fox Film Corp.