The Court of Appeal is expected to rule today on a T-shirt row between high street chain Topshop and singer Rihanna.
Rihanna claims the store used an image of her on a tank top without her permission.
An earlier court hearing ruled the 26-year-old pop star's fans might be deceived into thinking she had endorsed the T-shirt.
In the UK, celebrities have no legal right to control the use that is made of their image.
But if a product is marketed in such a way to incorrectly suggest they have approved it, then it can amount to "illegal passing off".
Topshop lawyer Geoffrey Hobbs QC, who is trying to overturn the previous ruling, argued there is a tradition of merchandising star images over the decades, including those of Elvis Presley, Jimi Hendrix and Prince.
However, Rihanna's legal team say the image used was from an unauthorised photograph taken while she was filming a music video in Northern Ireland and Topshop should be banned from exploiting it.
The Diamonds singer has various lucrative endorsement deals with retailers, including Topshop's rival River Island.
Mike Gardner, a partner and head of intellectual property and commercial at Wedlake Bell LLP, said: "Although each case is different, if Topshop fails to overturn the ruling, this may discourage other retailers from selling similar items in the future and may lead other celebrities to take a tougher line in policing their rights.
"But if Topshop is successful, celebrities and their management teams may have to think more about how they can best protect their branding in countries like the UK which do not recognise image rights."