A company which allowed customers to resell their digital music "second hand" breached copyright, a US judge has ruled.

ReDigi billed itself as the first legal way to resell music bought online - but soon provoked the ire of record labels.

It was sued by Capitol Records in January 2012, and on Monday a New York judge said ReDigi was making unauthorised copies of music.

The ruling could have broad implications for digital reselling.

Unlike physical music CDs, Judge Richard Sullivan ruled that the "first sale doctrine" did not apply.

The doctrine is a long-established rule which allows the reselling of goods to a new owner. In other words, selling a CD once you no longer want it.

But in the digital world, where duplication is much easier, the first sale doctrine was not appropriate, the judge said.

"It is simply impossible that the same 'material object' can be transferred over the internet," he wrote in his ruling.

"ReDigi facilitates and profits from the sale of copyrighted commercial recordings, transferred in their entirety, with a likely detrimental impact on the primary market for these goods."

ReDigi argues that their system means the original download is removed from the seller's computer.

The company asks users to download proprietary software, which verifies if a file was bought legally. If the song checks out, it is then erased from the seller's hard drive and uploaded to ReDigi's computer servers.

ReDigi's software is designed to prevent sellers from reinstalling a sold song to their computer, and offers users the chance to check their libraries for illegal music.

BBC News