A few lines of 'digital DNA' could allow the publishers of Harry Potter to find and finger the person apparently responsible for leaking the final adventures of the boy wizard.

A leaked version of what is claimed to be the latest Harry Potter novel, painstakingly photographed page by page, has been posted on the internet before the book's worldwide release on Friday and circulated via file-sharing networks.

But computer experts said today that the identity of the person behind the leak could be revealed by tracing the digital camera that was used.

Information contained on the photographs uploaded to file-sharing websites could provide a trail which leads back to the photographer, said experts at Canon, the imaging company.

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By examining the vital information - or 'metadata' - built into each photo, the company's technical officers have established the serial number of the camera that was used, which could in turn lead to the identity of the camera's owner.

The information, known as Exchangeable Image File Format (Exif) data, has already revealed that the camera used was a Canon Rebel 350. Because the model is three years old, the device would likely have been serviced at least once since it was purchased, in which case the owner's name would be known.

The serial number itself would not necessarily give away the name of the owner, Canon said, as it can only match serial numbers with owners if the purchaser registers the device after buying it. Every time a Canon camera is serviced, however, the serial number and owner are logged together.

"In theory, we can find out which country the camera was sold in and in turn the warranty and service centre records in that country could be checked," Vic Solomon, a product intelligence officer at Canon's UK head office, said. "It would take a lot of work, but there's a good chance they could find him or her.

"From what we know, the device is one of the original Rebel cameras, probably a 350D, and given that they've been out for three years, it's likely the owner would have had it cleaned or repaired in that time."

All that could be told initially from the number was that the camera was likely sold in either America or Canada, because the Rebel 350 was not distributed in any other territory.

Bloomsbury, the UK publisher of Harry Potter and the Deathly Hallows, the final book in the J.K. Rowling series, said today that its lawyers are investigating all potential leaks of material from the book and would take legal action wherever necessary.

Every image that is taken on a digital camera contains Exif data, which holds information about the picture such as zoom, contrast, focus and 'distance to subject' measurements. It is typically used for 'trouble-shooting', so an owner can ascertain why a picture may not have worked, but it also enables a court, for instance, to establish whether a picture has been digitally altered.

"The Exif data is like the picture's DNA; you can't switch it off. Every image has it. Some software can be used to strip or edit the information, but you can't edit every field," Mr Solomon said.

A post on the digg.com website claimed that the serial number of the camera which photographed the pages claimed to be from the unpublished Harry Potter, was 560151117.

Canon's head office in Japan confirmed that a serial number would reveal the country in which the camera was sold and possibly also the store, but declined to give any further information about the device used in this case.

The discovery reveals the extent to which people who distribute photographs online can be traced, which is especially relevant given the popularity of social networking sites such as Facebook, which have in some cases been sources of incriminating material.

If traced, the person who photographed the Harry Potter novel could be found guilty of copyright infringement, but would be unlikely to face criminal charges as the photos appear not to have been published for commercial gain, lawyers said.

"There are criminal provisions in copyright legislation, but they tend to be used in cases of obvious counterfeiting - such as selling fake computer games or DVDs in a car boot sale," Mark Owen, an intellectual property partner at the London firm Harbottle & Lewis, said. "If Bloomsbury were to pursue an action, it would more likely be a civil case, in which case any damages would be assessed according to the loss in book sales."

JK Rowling, the book's author, said she was "staggered" that "some American newspapers have decided to publish purported spoilers in the form of reviews in complete disregard of the wishes of literally millions of readers, particularly children, who wanted to reach Harry’s final destination by themselves, in their own time".

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