The standard for infringement in trademark law is “likelihood of confusion”. Specifically, the question of infringement is whether a junior user’s use of the mark is likely to confuse a member of the public as to the origin of the goods or services.

After Steamboat Willie is out of copyright, anyone will be able to distribute copies of it. If distributors use the mouse image in a way that confuses consumers into thinking their copies came from Disney, however, then they may infringe Disney’s trademark.