It's one of the most infamous artworks of recent years. Damien Hirst's For the Love of God, in which over 8,000 diamonds cover an 18th-century human skull, went on sale for a staggering £50m (Dh284m) in 2007 - an unsurprising price tag, perhaps, considering it cost a whopping £14m to make. It immediately divided opinion; detractors called it expensive, tasteless bling, while supporters, of whom there were many, waxed lyrical about Hirst's clever evocation of mortality and what the piece said about the morality of money.
But just weeks after the piece went on display, the artist John LeKay suggested that one of the 21st century's most discussed works wasn't really Hirst's idea at all. He alleged that it was actually based on a skull covered with crystals that he had had made in 1993. In the end, there was no legal claim - not least because skulls encrusted by precious stones have been around for thousands of years.
But, three years on, the wounds are clearly still raw. Last week LeKay spoke out again, giving an interview to the art magazine Jackdaw. In the article, no less than 15 separate claims of plagiarism were made surrounding the work in Hirst's glittering career, including eight new allegations. "Damien sees an idea, tweaks it a little bit, tries to make it more commercial," said LeKay. "He's not like an artist inspired by looking inwards. He looks for ideas from other people. It's superficial."
Hirst refused to comment. But he has been dogged by such accusations of plagiarism in the past. In 2000, he paid an undisclosed sum out of court when the toy manufacturer Humbrol complained that his six-metre bronze sculpture of a male torso - his first £1m work - was strikingly familiar to a much smaller model available in its Young Scientist Anatomy set. Even one of the works in his 1995 Turner Prize-winning entry (Mother and Child, Divided) bears remarkable similarity, LeKay claimed, to a page in a catalogue of science education products he once showed Hirst.
Does it really matter? As much as one can feel sorry for LeKay, struggling in the cultural margins while his sometime friend is banking millions, it's hardly new for a famous artist, musician or writer to be accused of such behaviour. As LeKay admits himself, the very reason these people are rich, successful and talented is often because they take the nub of an idea and hone it into something that has mass appeal. In that sense, Hirst's use of the Humbrol toy isn't so far removed from Warhol's famous soup can images - and no one's suggesting they're not interesting, original art, even though controversy has circulated around the provenance of Warhol's work too.
A sense of timing is also important: Hirst revealed For the Love of God to the world at the very moment vapid celebrity culture was at its height. Thirteen years earlier, when LeKay was sticking jewels on skulls, we were in the middle of grunge. In the art world it's rare to find work not influenced by anything that has gone before it. Even Picasso wasn't afraid of copying his favourites. A whole chapter of the Spanish painter's career features "stolen" images, in his case not from unknowns but from great masters such as Velázquez, Goya, Manet and Delacroix. But in every instance he added something new and intriguing to the original, and in the process offered a great quote: "Bad artists copy. Good artists steal."
The iconic pop artist Roy Lichtenstein probably empathised: he appropriated whole images from DC Comics' storylines, but by increasing their scale and changing their details, he changed their meaning and in so doing made some of the best work of the 1960s. Appropriation is a fully recognised artistic tradition stretching right back to Leonardo da Vinci, through Picasso, Duchamp and Warhol, although the protocol is that the source of inspiration is named.
Sam Leach, the winner of this year's Wynne Prize in Australia, failed to do so until more learned critics pointed out that Proposal for Landscaped Cosmos was, in fact, nearly identical to a 17th-century painting by the Dutch master Adam Pynacker. All of which begs the question: with art and culture so readily available to us these days, is it actually possible to be original anymore? One artist who can genuinely say he's unique is Nasser Azam: he has painted in zero gravity and in Antarctica. But even he admits it's difficult not to be influenced in some way.
"I experimented a lot with the styles of Picasso, Francis Bacon and Munch as a teenager," Azam says. "Looking back now though, what was crucial was that the underlying subject matter was always personal. So I think the techniques and the styles of famous artists are an important learning curve as you develop because they teach you how the influences of their times dictated the art that was being created. As long as you are only using this as a learning tool, it enables you to learn how to better your own creativity and how you capture it."
Azam says he would actually be flattered if, for example, someone went to Antarctica and made a piece of work very similar to his. But perhaps he might think again if they made millions of pounds from it? "Well, what makes plagiarism in art different from that in science or literature is that each piece of work is basically unique - no matter how hard you try you can never truly replicate a painting. So all art, in a way, has references to previous work - it's up to the artist how they use that."
And when the artist is as good as Damien Hirst at gathering together all their influences and ideas - borrowed or not - into spectacular, era-defining art, it seems churlish to criticise them for doing so.