The pair appeared to be kissing when they were pictured together in a nightclub in Paris, France, on Sunday night.
But the 40-year-old actor’s lawyers then sent out a warning saying he objected to the images being published and that he had a right to privacy under French law.
A photo agency offered the pictures, taken at the French nightclub L’Arc, to a number of publications in Britain. The images have yet to be published.
Media law expert Keith Mathieson, from the legal firm RPC, said French law allows for greater privacy restrictions than in the UK.
However, he said UK law already prevents ‘intrusive’ pictures of people in private activities from being published.
Mr Mathieson explained DiCaprio was likely to be arguing that he had a ‘reasonable expectation of privacy’ while he was in the nightclub.
Another media law expert, Gavin Millar QC, from the legal firm Matrix, explained that complainants can sue in France if a picture is taken in the country and then published in other EU countries.
He added that permission has to be sought from the person being pictured before the image is published – or face a fine.
However, pictures taken in ‘familiar circumstances’ – such as a politician going about his work – are acceptable, he said.
‘The problem comes when the pictures is telling you something about a person’s private life,’ he told MailOnline.
‘(Leonardo DiCaprio’s) case is not untypical. In France, there are established privacy laws and in Britain they are still evolving.’
DiCaprio and the singer were rumoured to have dated last year, enjoying a brief romance, and the pictures sparked reports they may have rekindled their relationship.
But according to TMZ, there is nothing going on between the pair.
The website reported Rihanna was at the venue with Cara Delevingne, and when they saw the actor there was a friendly greeting which included a kiss on the cheek.
It said the rumours of the pair getting very friendly were down to the photo being at a bad angle.
DiCaprio has been in the French capital promoting his latest movie, The Revenant.
It is not the first time he has turned to French law.
Last year he sued Oops! magazine for claiming he fathered a child with Rihanna and told the singer that he did not want the baby.
He demanded the magazine retract the story and pay him the maximum compensation French law allows, namely of 18,000 Euros, or around $US20,000 in damages plus legal fees.
The cover of the May edition featured pictures of Rihanna and Leo saying, ‘Rihanna Pregnant With Leonardo’s Baby: He Doesn’t Want The Baby’.
The French court ruled in favour of the star finding not only were the claims false the publication of two paparazzi pictures of the Wolf Of Wall Street star breached France’s very strict privacy laws.
The star did not get the full compensation he was asking for but was awarded 8,000 Euros – which is just over $USD8,800 – in damages and legal fees.
The issue of France’s strict privacy laws have surfaced in a series of high profile cases in recent years.
In 2014, French President Francois Hollande claimed he was entitled to privacy amid allegations he was having an affair with actress Julie Gayet.
And two years earlier there was uproar after pictures were published of the Duchess of Cambridge sunbathing topless while on holiday.