WASHINGTON — The Supreme Court on Wednesday set aside a $3.4 million award to a victim of child pornography who had sought restitution from a man convicted of viewing images of her. That figure was too much, Justice Anthony M. Kennedy wrote for a five-justice majority, returning the case to the lower courts to apply a new and vague legal standard to find a lower amount that is neither nominal nor too severe.

The victim in the case said the majority’s approach was confusing and meant that she might never be compensated for her losses.

The two dissents to the majority opinion would have taken more categorical approaches. Chief Justice John G. Roberts Jr., joined by Justices Antonin Scalia and Clarence Thomas, said that restitution was a worthy goal, but that the federal law at issue did not allow awards when many people had viewed the images.

Justice Sonia Sotomayor took the opposite view, saying that each viewer could be held liable for the full amount of the victims’ losses.