Mr Justice Birss said Topshop's sale of a Rihanna T-shirt at the centre of the dispute was an act of " passing off".
But he said the "mere sale" of a T-shirt bearing the image of a famous person was not necessarily an act of "passing off".
He said a "substantial number" of buyers were likely to have been deceived into buying the Rihanna T-shirt because of a "false belief" that it had been authorised by the singer.
The judge said that was damaging to her "goodwill" and represented a loss of control over her reputation in the "fashion sphere".
He said it was for the singer not Topshop to choose what garments the public thought were endorsed by her.
More top news
A minute's silence will be held across the UK at midday to remember the victims killed in the Tunisia beach attack a week ago.
Jim Carrey apologises after using a photo of an autistic boy to promote his claims vaccines contain harmful neurotoxins
Newly released files show a proposal to move the population of Hong Kong to Northern Ireland