This is what is known as "innocent infringement". In the US, you have reduced liability but not none. You would be liable for the actual damages (e.g. the cost of a copy, or however many copies were improperly obtained), and for statutory damages which the court can reduce to $200. This assumes that the party reasonably believes that they have permission. This happened to the US Postal Service, which is now being sued for 4 billion infringements of an artist's copyright, apparently because somebody didn't correctly distinguish between a picture of the Statue of Liberty and a modern version.
(There is apparently some confusion over Davidson's lawsuit against USPS. USPS distributed stamps reproducing Davidson's sculpture, without his permission, on the mistaken belief that the image was of the actual Statue of Liberty. Sculptural works are protected by copyright, and permission is required to create and distribute a derivative work. For a very similar post stamp infringement case involving a different sculpture, see Gaylord v. United States, 595 F.3d 1364). In that case as well, USPS did not get permission from the copyright holder. The photographer received permission from a partner in the firm that constructed the memorial in question, but the firm did not hold copyright in the infringed sculpture. USPS was then referred to the partner for permission to use the underlying work. The USPS's unsuccessful defense was based on fair use, not innocent infringement. Substantial damages were awarded to Gaylord. The outcome of Davidson has not been determined, and again, will not hinge on innocent infringement, but might hinge on fair use, or on a classification of the sculpture as part of an architectural work. It is not clear whether the photographer who took the photo in the Davidson case had permission from Davidson).
