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(Pocket-lint) - Amazon has acquired a patent that could allow it to form a marketplace for the reselling of digital content. That means you could list your unwanted MP3s, eBooks, applications and video files and sell them on for credit - perhaps in Amazon Coins - or cash.

The patent does not mention whether copyright owners would get any slice of the action - presumably Amazon would - so it could open up a legal can of worms should Amazon go ahead with the idea.

Called "Secondary market for digital objects", the patent essentially covers the transfer of digital content in one user's "personalised data store" to another's.

"An electronic marketplace for used digital objects is disclosed. Digital objects including eBooks, audio, video, computer applications, etc, purchased from an original vendor by a user are stored in a user's personalised data store. Content in a personalised data store may be accessible to the user via transfer such as moving, streaming, or download," it reads.

"When the user no longer desires to retain the right to access the now-used digital content, the user may move the used digital content to another user's personalised data store when permissible and the used digital content is deleted from the originating user's personalised data store." 

Amazon does suggest a fail-safe, however, to avoid the content being transferred again and again. "When a digital object exceeds a threshold number of moves or downloads, the ability to move may be deemed impermissible and suspended or terminated," the patent states.

The patent also includes the selling of playlists or groups of content, such as an entire music album. "Additionally or alternatively, a collection of objects may be assembled from individual digital objects stored in the personalised data stores of different users, and moved to a user's personalised data store."

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Amazon already offers a form of digital content lending in its Kindle Owners' Lending Library, where Prime subscribers can borrow a book from the hundreds of thousands on offer and swap it for another when they are done. However, this patent could tread on more shaky ground, one that is already being legally challenged in the case of US digital music reseller ReDigi.

ReDigi is being sued by EMI for a similar thing. It allows users to sell their iTunes music files. The service claims that, in doing so, it is no different from allowing customers to resell their CDs - something not against the law in the US or in many other countries. However, EMI claims that it is impossible to know whether the seller, in that instance, will have had the file deleted from their system.

In terms of cloud storage, the solution for Amazon would be more simple. If a user has access to the cloud version of a particular file, but is not able to download it, or it is downloadable only with strong, locked DRM, that could in effect become inaccessible when transferred to another user.

After all, if somebody buys a CD (or DVD) and rips it to their computer for personal use then resells it, is that not worse for the original copyright holder?

Where the marketplace could be even less well received is with independent app developers, who rely on the profit of each sale to make their living and to develop new applications. The videogames reselling business, for example, has been blamed in the past for creating a market where only major publishers can make money - it's a market that has seen many casualties over recent years, including THQ.

Even the major publishers are taking action to make money from "pre-owned" games and offer incentives to buy the original version. EA games, for example, often has the multiplayer and online pass free in the box, but charge handsomely for it if the one-off code has already been used.

For now, this just a patent for Amazon. The difficult part comes in trying to implement it.

What do you think? Would a marketplace to resell your digital content be a good idea? Would it help combat piracy? Or will it serve only to hurt independent developers and studios? Let us know your thoughts in the comments below...

Writing by Rik Henderson.